That's easy: the mix of puke, stomach acid, bits of whatever you last ate and the last couple of drinks and beer/wine you had, because you're damn sure not wasting that precious alcohol!

Another one: the room temp leftovers of all the beers and other drinks from the night/weekend poured into a pint when you're cleaning up. The Hangover Special! Yummy. Bonus points if there's a cigarette/joint butt in there somewhere that you fish out because you didn't notice someone had used that can as an ashtray. Delicious!