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1.
a magical feat often depicted in pornos where a both a female's vag and poop shoot are pounded simultaneously

also known as: double penetration; one in the fridge, one in the freezer; mr. jones, mr. anderson; double stuffed; and ball banging (bc the dudes balls often touch)
when we proposed the over under to gina, she smiled, dropped her draws, and said "lets get ballz deep".
by ballzdeep April 12, 2005
 
2.
Another term for the 69 sexual position
That dog belly bitch was overunder with nick at the 7/11 while selling mescaline to the Cuban hobos at their white teeshirt party.
by Flo (like the show) April 12, 2011
 
3.
if your don't want to touch the person you are stuck sleeping with and there is two blankets and one bed. One person goes under one blanket and the other goes on top of the blanket next to the other person with a blanket over themselves. Super safe way to ensure no funny business in the sack.
Straight person 1: Well, were stuck sleeping on the cot again.
Straight person 2: At least theres two blankets so we can over-under.
by jimboneslamboni December 18, 2011