When you jack off for so long that your knees feel really weak and you can bearly stand

as in beg for forgiveness

a phrase often used by wild, drunk, country girls while being plugged by highschool linebackers when they cant seem to hit the right spot

Masturbation. Another one of those long, drawn out and funny ways of saying you masturbated.

Depending on context, it could also be used as term for giving/receiving a handjob.