nut sack deep double stuff (NSDDS). it is when achieving nut sack deep penetration one also inserts his scrotum into the vagina. This is the ultimate level of penetration by a male.
Tanner: Dude i was powning this chicks vag last night and she was down with letting me go NSDDS.
Brian: WTF is NSDDS?
Tanner: it is when i go nut sack deep on a chick and then lshe ets me shove my ball sack in her vag as well. really a delightful yet painful experience for the both of us.