I get that Artificers' spells are actually just little creations and such. Thus I get why Artificers get so many tool proficencies:

Woodcarver's tools: You carve a magical item out of wood, you carve symbols into wood, etc.

Smith's tools: You make stuff with metal, you modify metal stuff, etc. 

Tinker's tools: Duh

Alchemist's supplies: You make potions and elixirs

... and then there's Thieve's Tools, which every artificer gets at level one. How do you flavor with Thieve's tools? Thus far, I've just used the excuse that Theive's Tools are just mini Tinker's Tools, and thus that's the sort of flavoring I go with, but how do you flavor for Thieve's tools? 

I mean Thieves' Tools are just mini Tinker's tools (scissors and pliers can do a fair bit of tinkering). So that's a solid reasoning for using them like Tinker's tools.

But I guess if you want to go down a more thief-flavored route... you could consider it to be a literal expression of unlocking magical potential from the weave itself. Magic exists everywhere within the air and world around us all just below the surface of reality. With the right knowhow and skill (and a little application of the arcane equivalent of elbow grease) you can pick open the lock that prevents magic from just spilling out into the everyday. Most spellcasters do this with incantations, gestures, spell slots, and arcane foci, holy symbols, etc. For you the unlocking isn't a metaphor, you literally pick the lock on magic and unleash a single spell into reality before the door to the arcane slams back shut again.

This set of tools includes a small file, a set of lock picks, a small mirror mounted on a metal handle, a set of narrow-bladed scissors, and a pair of pliers. Proficiency with these tools lets you add your proficiency bonus to any ability checks you make to disarm traps or open locks.

I mean there isn't anything inherently malicious about thieve's tools. I imagine maybe artificer's are inherently different than a normal craftsman because like all classes they train for adventuring and thus thieves tools are useful when exploring dungeons. You could come up with your own arbitrary reason but it gives another class that can help spot and remove traps as well as help with hidden treasure.

Thieves' tools are also used for MAKING traps according to Xanathar.

Thanks. That's what I thought, I just think it's kind of weird that that's the one they chose to give you at level one. I know they're not malicious in nature, but they're still designed to open locks and such. These are all great suggestions, though. The arcane key thing in particular is really creative! It wouldn't make sense for this character, but I might use it in the future. 

The rogue is the burglar.  The artificer is the locksmith.

I would say you use them to unlock the magic in your surroundings, and use it against your enemies

Thieves' tools are excellent for any kind of investigator who wants to enter a place without having to break down a door and is also good for disarming traps.

Here's Keith Baker on how an artificer's magic might manifest from different tools.

http://keith-baker.com/dm-artificer/