A thumbnail sized image of an attractive person that clicks to a larger version of said person, where they are revealed to actually not be as attractive as they looked in their smaller image.
Man, that friend of yours on Facebook is a real thumbabe, but then i clicked her pic and saw what she really looked like.
Implies gratitude, acknowledgement and departure all at once. Often used at the end of a quick online conversation in which one asks someone else for a favour.
Person #1: Hey man can you write my essay for me by tomorrow? It's about the HungarianRevolution of 1956 thxkbai.