did you see the man in the trenchcoat, doing the batjack from a lamp post?  he was batjacking on the chin-up bar
the act of masturbating while hanging upside down, as a bat would hang from the ceiling
"did you see the man in the trenchcoat, doing the batjack from a lamp post?  he was batjacking on the chin-up bar" What is the definition of "batjack"?