I'm relatively new to D&D 5e & I just wanted to run a possible attack idea before my next session as it's really out there (potentially rules breaking).

I'm currently playing as a Lv 2 Copper Dragonborn Paladin.  I'm planning on having our group's bard cast Charm on an enemy (ideally BBEG) to actually kiss me -- On the bard's action, could I assist with a little flirting (Persuasion Check to boost)?

ASSUMING the Charm is successful, could I move towards the affected enemy (on my turn), kiss them (going for a lip lock) & immediately use my acid breath attack on the enemy?

Should this action be allowed, how should it be resolved?  The acid breath attack deals 2d6 (Dex save DC 12) in a 30 ft. line.  HOWEVER, since the attack is done at point-blank range & being directed specifically at the enemy's internals...  I would reason that it would deal 12d6 (2d6 x 6 spaces worth) with a CON save DC 12 since it would be impossible for their internal organs to dodge the attack for reduced damage. -- This is one part the would be up for debate with my DM & just want to get some thoughts on resolution.

ADDITIONAL: Could I use Divine Wrath (to add 2d8) as my bonus action? -- If I read this properly, it should be allowed RAW since the above mentioned is an unarmed attack.  Just want to see if I can add a little extra punch to this unconventional attack.  This is something I'm willing to drop if I'm overextending my actions for my turn.

FINALLY, would there be any alignment consequences for attempting this? I'm currently NG & the goddesses I'm working with are LG (Therin; Life & Light) & CG (Tymora; Good Luck).  Since I'm Lv. 2, I haven't taken any oaths yet (& would likely have to get a related cleric involved)... would either goddess consider this an evil act (that could anger them) OR would they possibly be impressed with such a bold & risky move (something that Tymora might like)? -- If this does carry negative consequences for my character, could they get away with the one-shot?

Thanks in advance for any insight you can provide regarding this idea.  My character is running a little ragged after our last session (unable to complete a long rest due to party pre-emptively invading an enemy stronghold) & interested in making the final battle quick, if possible. 

All of this is going to have to be things you discuss with your DM.  I'm assuming you're using the 2024 rules, since your Divine Wrath (Divine Smite?)  seems to be costing a Bonus Action in your description.

Rules as Written, even a creature that's large enough to take up the entire space of your full Breath Weapon still takes only the normal 2d6. A creature that has swallowed you still gets a Dex Save for half damage against your Breath Weapon under standard circumstances. As described, at best, you've decided to use an Unarmed Strike /Grapple, and the Grappled Condition doesn't affect DEX saves. 

Also, Charm Person and Charm Monster aren't cinematic mind control. If Successful, they would make the BBEG Friendly to the Bard,  and more persuadable, but if the BBEG doesn't want to kiss this Paladin that they're still hostile to, and still in the middle of fighting, that's an insanely hard sell to anyone, probably enough for the DM to say, "No, he's not going to do that, don't bother rolling."

Divine Smite only works on attacks. If you didn't make an attack roll, it's not an attack. An action that only imposes a Saving Throw (such as using your Breath Weapon) isn't an attack. Unarmed Strike / Grapple isn't an attack either (Unless done as part of the Punch-And-Grab feature from the Grappler Feat, or something similar) so no Divine Smite there, either.

Edit 2024 Suggestion or 2014Suggestion could force the kiss, but it's unclear what levels your party is at. I'm also more unclear what version of the rules you're using (2014 or 2024), because the Breath Weapon features you're listing are for the 2014 PHB Dragonborn. Please specify.

In short, no, you can’t. The kiss would not matter. Enemy gets a save as usual, damage roll as usual. 

Besides that, there’s lots of problems. If the bard charms an enemy, that charm effect would only apply to the bard, not you (at least that’s how most charm effects work, it would depend on the specific one used). Also, charming someone has specific effects. It does not make them suddenly physically attracted to the charmer. It just basically means they won’t attack you. 

Your breath weapon, and indeed any sort of attempt to damage another creature, can not target a specific part of the enemy. It’s all abstract. It certainly can’t target the inside of a creature. Moreover, you can’t simply decide to try and stack all the damage from an AoE onto a single space. The breath attack will fill its space as normal. Damage as normal.

As notovny says, your breath weapon is not an attack; only things that make an attack roll are an attack. Things that force a saving throw are not an attack. I understand this is counter to logic and the common sense understanding of what it means to attack something. But in this case, it’s a defined term in game, which overrides the more typical definition of the word.

Alignment consequences will be up to your DM. However, as alignment is all but meaningless in this edition, so are consequences for changing it. Unrelated, but paladin oaths don’t have to involve a god. Some tables play that way and, of course, they should if that’s what they like. But in this edition, by RAW, a paladin doesn’t have to have anything to do with any gods. If the action might break an oath is a different question, and would depend a lot on which oath you’ve taken. But as you haven’t taken a subclass, and therefore have no oaths to break, you’re probably fine.

Current Vibe: Not worth the hassle / HIGHLY unlikely to work as desired

I was probably over-optimistic on effects, but I would still consider it even with a potential being half the ideal.

From what I was reading about Charm Person was that it wasn't focused directly on the bard themselves, but the party in general.  HOWEVER, the enemy would get advantage on their saving throw if the party was actively attacking them prior to the spell being cast.  If the spell was successful, they would be friendly towards the party until attacked OR spell duration ends, at that time the target would notice they were charmed (which would automatically revert them to hostile towards the party).  With the idea that the target wouldn't object to receiving a kiss in that charmed state, as it would seem innocuous to them.

As for the breath weapon, the damage logic seemed reasonable as it was being inflicted in a limited space & would be a bit more concentrated than normal.  However, I'm willing to concede some blowback as the target can only take so much pressure before the excess has to dissipate to the environment.

As for Divine Wrath, this was wishful greed into stacking damage.  However, if the breath weapon isn't a targeted attack, I wouldn't be able to utilize it as a bonus action.

In regards to version, most characters were drafted with the 2014 rules on paper, but half the group (including myself) transferred their character to here while the other half are utilizing a 3rd party app... so 2024 content could have unintentionally leaked in.  Additionally, Death Saves are NOT being RAW...  besides being a DOUBLE-BLIND roll (only the player knows the roll & the counts), a critical success is only being treated as a double-save (instead of instant recovery) & ANY DAMAGE while down is counted as a DOUBLE-FAIL (vs a single fail on the save count).  I have lodge an objection to their ruling of their system, but haven't bother going full rules lawyer on it since my character hasn't been subjected to the Death Save system yet (as the group has managed to get a heal in prior any rolls) & I just wanted to keep the game moving (not worth the hassle / picking battle wisely).  Our group DID manage to keep a departing party member alive (barely... in spite of the DM's stated intentions, as one player was swapping characters & was perfectly OK with the character death).

The only other side note is the DM is one of the bartenders we're playing at (as part of their Tabletop Night) & want to stay on friendly terms.

I do appreciated your 2 KB on the idea as it would have been something that might have been epic to pull off, should the arguments be in my favor.  HOWEVER, such reality checks does help ensure I'm not derailing the game with seeming impossible (or at very least excessively improbable) schemes.

Again, that’s not how Charm Person works. Spells, powers, etc. do only what they say, exactly what they say. Breath weapons can’t not be concentrated, because there is nothing that says they can be concentrated. The spell Charm person says:

On a failed save, the target has the Charmed condition until the spell ends or until you or your allies damage it. The Charmed creature is Friendly to you. When the spell ends, the target knows it was Charmed by you.

That’s all it does. When it says “to you” that means the caster. It does not apply to the rest of the party. Please also follow the links to the conditions it imposes. They only do what they say. “Charmed” means they won’t attack the charmer, they can freely attack anyone else. “Friendly” says it regards you (again, the caster) favorably. That’s doesn’t mean they want to kiss the caster, let alone the caster’s friend. It means you (the caster and only the caster) get advantage on checks to influence them.

As far as the death saves, that’s a house rule, clearly designed to reduce metagaming, and whack-a-mole healing. And if it was clearly communicated at the start, there’s nothing wrong with it.

I appreciate you wanting to use powers creatively. But there is no conceivable rules-based argument you can make which will allow it. But, hey, in the end, it will be up to your DM if they want to allow it, go ahead and run it by them. Just keep in mind if they do allow it, the monsters will be able to do the same things to you. 

There's also the always-effective counter to players wanting to make their abilities stronger than they should be: sure, you can adjust your breath weapon so it goes into a person's lungs - but that means that enemies can do it to. A caster only needs line of sight to cast Cloud kill within range - the second you open your mouth, they use their held action to cast it down your throat. 

Shenanigans are fun to do every once in a while if there's a conceivable argument for it in the spell/ability description. However, if you're trying to bend the rules a LOT to get your desired effect, then generally speaking a DM will say that the enemies can bend the rules in the same way (and then it becomes a DM vs PC game and that's bad in a whole different way)