'weenis' is the extra skin on your elbow
'butt' is your gluteus maximus, or for you idiots it's the ass
therefore when combined it is the extra skin on someones glutues maximus.
usually used when insulting someone or just complimenting them.
1. A fag's dick.
2. A term that is often used similar to the term asshole or jagoff when describing a person who seems to be perpetually loud, obnoxious and rude.