So Finn and Poe's relationship is developing nicely but just before they start making out for the first time, Poe stops Finn and explains that he's not actually human, just looks like one for the most part, it doesn't change anything, but the reason he's explaining this is the fact that he has fangs and he doesn't want to freak Finn out with them.

Up to you if the reason Finn's never noticed them before is because Poe is just that good at not flashing them, or they 'drop down' when Poe's having emotional extremes, or any other reason you can think.

Lets not have him be a vampire and drink blood, he just has these fangs (a no longer needed part of his species evolution? idk).