Combination of shit and fap (
mastrubating), as in
mastrubating while
taking a dump. Side effects unknown.
Ewan: Dude, I just shitfapped BIG time...
Lloyd: ZOMG
WTF? You're disgusting!
Cindy: I think shitfapping guys are SOO sexy... It's like, you know... You like, get it all out?
Ewan: Totally...