It's generally used in a sexual nature giving way to what a mans Trousers Cover up, i.e. the male genitalia.
It could also be explained as a corruption of the phrase "One eyed Trouser Snake" Which refers to a mans Wang.
That Chick last night wouldn't give me that time of Day so I grabbed her hand and put it on my Trousha.
Does anyone want to touch my Trousha.
That Guy is a dirty Trousha
Thank your mum for cleaning my Trousha
I told that chick to suck my trousha even though she looked like a smashed bag of assholes