Best definition
A crude way to say you received a handjob. Based on different techniques, it makes sense to call it this

because of the similar application of torque.

Hey Billy! Tell these guys about your date with Suzie the other night!

Man oh man! We didn’t even make it through the previews when she pulled out my fat boy and started wrenching on me right in front of God and everybody! Whew! That was a good old fashioned wrenchjob.