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2.
Pump your pecker in and out of a girls ass cheeks.
1. get a stiffy.
2. compress her ass cheeks.
3. insert your stiffy between cheeks.
4. pump stiffy in and out of cheeks.

Note: lubricating the cheeks facilitates pump action. "its like titty fcuking but with her ass cheeks". alternative to penetration.

"If she doesn't have big tits then try slip dogging"
by UHPIKE August 29, 2007
 
1.
When a man slides his penis between his partner's buttocks cheeks, but does not penetrate. Similar to "titty-fucking," but instead involving the butt cheeks.
Brad didn't feel like penetrating, so he decided to try slipdogging instead
by Laura from Ohio January 23, 2006