Simple congregruity of 'tri', meaning third and nipple. The correct adjective for a third nipple. Can be pronounced 'try-nipple' but 'trin-ipple' sounds funnier.
Ozzie: Hey, did you see Lily Allen whip out her trinipple?
Keith: No,
Ozzie: Yeah, it was almost down her stomach
Keith: What, like a dogs?
Ozzie: Yeah.
Keith: Does that mean she's part canine?
Ozzie: Hell yeah.
Keith: I'd wouldn't say no to fucking that.
Ozzie: But she wouldn't say yes to you. Dogs still have class. And you're her Dad
Keith: Oh, yeah, still would though. (They high-five eachother.)
Ozzie: (Under his breath) Prink.