When the male of the species behaves in such a lame way that it is likened to the female of the species.
The internationally recognised symbol for this is the act of holding your hands in front of your crotch with your thumbs and fore fingers touching in a triangular shape.
Rupert - Hey Luke, where's your buddy James?
Luke - Oh he's gone for a facial.
Rupert - He's such a Trouser Triangle.
Luke - James smashes his car up every time he goes anywhere. He drives like a woman.
Rupert - Yeah, he's such a Trouser Triangle.
Luke - James isn't drinking tonight, I think he's grown a vagina.
Rupert - Yeah man, you know why though...(Rupert makes the internationally recognised Trouser Triangle Symbol)
Luke - Yeah - he definately is.
Rupert - James is such a Banter Biter, I ripped into him earlier on Urban Dictionary. He got cross and he has been sulking since.
Luke - Yeah. He's a trouser Triangle.