JFYM is an acronymn that stands for "Just Fucked Your Mom"
Oh man... I hate to break it to you but, I JFYM...

or the alternate Just Fucked My Mom form
WTF MAN!?!? DID YOU JFMM?!!! I'M GONNA KILL YOU ITCH
by Gygaxis June 4, 2004
Get the JFYM mug.