Teethpick

It's not the worst thing that could happen on your first day!

I don't think a lettuce stuck in your teeth should make you worry about leaving a bad impression. It's no big deal

I feel like this more appropriately suites the "nearly FML" category. If lettuce stuck in someone's teeth has become the face of FML, there needs to be a serious quality check on this site. As for this FML: shit like this happens daily. Food stuck in your teeth has a terribly small effect on a first impression, believe it or not. I think you're thinking this whole thing over more than anyone you introduced yourself to today.

That was crappy on their part, NOT ONE person could have pointed it out? Shoot, I've pulled male strangers aside and quietly told them to fix their fly

"Oh, hey, did you meet the new girl?" "…yeah." "What was your impression of her?" "Terrible! She had a piece of LETTUCE stuck in her teeth!" "OMFG! LETTUCE? Can we fire volunteers?!"

Most people usually let you know if you have something like that stuck in your teeth. So either they're all dicks who wanted to see how long it would take for you to notice, or most of them didn't even notice it themselves.

Too bad Deadpool wasn't there, I bet he'd tell you

Don't worry. Use it as a joke to break the ice in future conversations. Being self-effacing is a good thing in this situation and this is a good and harmless way to do so. You are doing an amazing thing, and shouldn't let such a small thing embarrass you or get you down. If, on the off chance, you encounter someone who wants to make it a larger thing, it will reflect poorly on them, not on you.