A nipple that is so long it actually resembles a penis, and in some cases is large enough to penetrate orfices repeatedy as a penis would be used.
Bob: Damn John, shaniqua's nipples are about to pop out of her shirt. I bet you she's got penipples.
John: Oh yeah, shaniqua. Lumberg fucked her. He said her penipples are out of control! She bangs people with them all the time!