What were those reasons? 

Quote from GracefulLion >>

Story time. So I was having my players fight three werewolves, nothing special. Our bard rolls a one to hit, and he's already pretty banged up. Me being me, I gave the poor boy mercy. Sort of. Instead of him dealing damage to himself or another PC, I instead have him cut his belt with his dagger, making his pants fall down. This didn't have any actual effect on the combat (as he kept missing, he didn't have a good day), but was still pretty funny. So, how do you guys deal with a nat one in combat? Is what I did valid?

When I player gets a nat 1 at my table in combat, I generally do nothing other than declare their attack or skill check either a complete failure or a miss. Sometimes I'll describe it as if they're flailing about blindly or making themselves look like a fool by swinging at thin air instead of the enemy, because that can be funny and it has no mechanical impact.

What you did seems to have gone over fine. It doesn't have any mechanical effect but it certainly does have a big flavor and roleplaying one. I would be quite hesitant to have a PC get pants in any game I run because you don't know if someone at the table has been pantsed or just generally dislike making jokes about a rather nasty form of bullying. However, it always depends on your table whether or not something is humorous or horrifying and this seemed to have worked well so there's nothing to worry about then.

You seem to be implying that you generally have harsher consequences for natural ones. It may be just me, but I dislike the idea of punishing nat 1s because Warriors get a lot of them and missing always stinking. Missing and wonking yourself or another party-member by accident feels worse. That being said, lots of good Dungeon Masters do have mechanical ramifications for nat 1s and that does add variety. So having mechanical consequences for nat 1s isn't something I would do or recommend, but it is at least a viable option.

EDIT: Huh I had no idea that I said all this in less words two years ago LMAO.

It's interesting. I read a bunch of these comments, (only page one) and I actually don't do what most people are saying. I have several groups, and have 'visited' several groups, and how we deal with nat1s almost every time, is the enemy than makes on oppertunity attack, assuming it makes sense with the weapons they have and such. We never allow two in a row.

If the player or the monster rolls a nat one whoevers in melee range gets an opportunity attack. For example paladin is fighting minotaur, minotaur rolls nat one paladin gets opportunity attack and vice versa.

Quote from gnomeman555 >>

If the player or the monster rolls a nat one whoevers in melee range gets an opportunity attack. For example paladin is fighting minotaur, minotaur rolls nat one paladin gets opportunity attack and vice versa.

As long as all your players are fine with that, then that's ok for you. But I'll re-iterate an earlier post and just say that adding a bad effect to a nat 1 attack roll 'punishes' players with classes that get Extra Attack more than other players (this example is only for melee range combatants so is specifically unfair to those playing martial classes that want to get up close-and-personal).

Personally I wouldn't do anything like this, because I think players would either get annoyed that their character is getting punished more than others, or it would simply encourage players to not play half the classes in the book because of the unfair disadvantage this gives.

We have it use the enemies reaction, and they can choose if they do it or not. And they don't get any extra attacks.
Not to mention the players also get this if the enemy rolls a nat 1.

I love Nat 1s because no matter what the armor class and proficiency bonuses and such, they miss. A miss and a Nat one are mechanically the same, but you can make jokes about how horribly the player or enemies missed for the rest of the session. For example when the enemy was prone and one of my players got two Nat 1s in a row. We joke about that until this very day.

If it is for a melee attack they miss and accidentally hit themselves taking 1d4 damage

for a ranged attack, it hits an ally

I have a magical item in my campaign which takes effect when the player rolls a natural 1. It's a cape, and if they roll a nat-1 to hit, they get all tangled up. It has an effect on them (could fall prone, half speed, attack with disadvantage, become blinded, etc) but it also has an effect on those nearby - namely, they need to pass a wisdom save or they start laughing.

Interestingly, this item seems to breed bad rolls, specifically for the wisdom save. Most people roll single figures, and it makes for memorable moments.

As such, I don't have nat 1's do anything unless it's convenient, and then only occasionally. Most of the time, they will just miss. Occasionally they will do things like cut ropes or alert people. I almost never have them hit the wrong person, unless it's absolutely plot-relevant for them to do so and it relates to their decisions - nat 1 when shooting someone with a human shield, for example.

As a rule, I don't punish people for making bad rolls; I reward them with adverse story conditions when they make poor choices.