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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.
by Tanner W. November 02, 2010