A Light Butt（しりがる）

He Says:
sirigaru　（しりがる）=slut
Usually slut means for women, so Japanese say sirigaru onna(girl) too.
You can use both sirigaru and sirigaru onna.
Both are the same.
The original meaning of sirigaru is light butt(siri=butt,garu=light).
So the word was made by the girls who can turn their butts to men easily for sex.

She Says:
This made me giggle when I saw it because I thought that they were using "garu" as "girl" which is a common thing to do. So I thought it was "butt-girl". Unfortunately it's not...but that might be a way to help you remember the word!

The next word is...やりまん。