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A guy who is only kept around for sexual purposes, with no serious romantic or emotional connection. Unlike a friend with benefits, a penisfriend's only function is to respond to bootycalls--an actual friendship does not not exist (but one may develop as a side effect).

A dildo with its own life.
My roommate's trying to take it slow with this new guy she really likes, so she's got a penisfriend on the side to vent all of her sexual frustration.
by HLRP March 15, 2011