WTF = What the F**K (duh)
As in: Ummmm WTF are you talking about?! [exasperated look]
IDK = I don’t know
As in: IDK who I text so much to be this over 1,500 texts a month!
FML = F**K My Life (also used as FYL, FTL, FHS…)
As in: http://www.fmylife.com/
KYS = Kill YourSelf (harsh, I know)
As in: You put wigs on your cats? KYS