To be interrupted while performing the act of masturbation.
I was jerking off last night and got interrupted by someone. He was masturhatin'.
To walk in on or otherwise prevent another's act of deeding/fingering.
Steve: *jerking off*
Bob: *walks in*
Steve: DUDE! I WAS ****ING JERKING OFF, YOU MIND?! QUIT MASTURHATIN'!