To rub your scrotum on something, as seen by the scene in the movie "Stepbrothers" starring Will Ferrell and John C. Reily, where Will Ferrell's character rubs his ballsack on John's drumset.
Simaliar to teabagging.
I just STEPBROTHERED your face.
Pfft. Only noobs stepbrother after a double kill.
I just was caught Stepbrothering.