Nut Knuckles

When a man masturbates and ejaculates and the sperm (a.k.a. nut) runs down your knuckles of the hand of which he was mastubating with.

Joe: Hey man did you fuck kelly last night?
Drew: Nah, bro she said she didn't want to at the last minute.
Joe: Damn that sucks. So what did you do then?
Drew: Well since she gave me blue balls I had to masturbate to relieve stress, and I accidentally gave myself Nut Knuckles.
Josh: You didn't have to tell me that.
Drew: Hey man you asked.