Twink I’d Like To Peg.
A TILP is a twink (a young, attractive, slim, gay man) who you would like to engage in sexual intercourse with, specifically pegging (the sexual practice where a woman performs anal sex with a man, usually using a strap-on or dildo).
Short-hand for the word floccinaucinihilipilification, meaning the estimation of something as valueless (encountered mainly as an example of one of the longest words in the English language).