An acronym meaning "that's so funny"
Used in place of the over-used "LOL"
Nicole: my dad just lost a game of wii tennis to the dog
Diandra: seriously?! Tsf!
Nicole: yeah, I blame it on his fat Italian-ness:-p
(please keep in mind that Italians should not be offended, her father really is fat and Italian, and she mentions it a lot :-]