When a
guy spanks or slaps another person with
semen on his hand - i.e. just after masturbating.
This is a generally condescending move on
par with tea-bagging, and - if executed properly - causes considerable distress on the recipient's end. Do not attempt this on someone that is physically stronger than you because they will perceive it as a sign of great disrespect.
"
John was being a
real douche last night, so I jerked it to a picture of his girlfriend and then spunked him in his sleep."
"Dude, knock it off or I'll
spunk you."