short for bat as fuck, this is a new way for youngsters to say "batty" or super batty, in fact.
Dude devin, you are bat af right now.

OMG... Maddy, you are bat af, you don't have to frikin yell every time in the classroom.

Dude did you see that, Devin was being totally bat af when he asked all those girls out?

Babyface is bat af everyday
by Mr. Cluckerz November 18, 2016