WTHDYTIA
Acronym for "WHO THE HELL DO YOU THINK I AM", a catchphrase from the anime Tengen Toppa Gurren Lagann. Said a gratuitous number of times by Kamina, Simon, Kittan....okay, EVERYONE in the whole d-mn series. This is a common abbreviation used on social networking sites (okay, and 4chan) to condense the phrase.
Every time Kamina says WTHDYTIA, you know something f---ing awesome is about to happen.