what most people say instead of "avonside" (an urban, all girls high school in Christchurch, New Zealand) the girls who go there are often pretty and like to go to parties and hookup with hot guys who often go to shirley boys or sometimes christchurch boys high
boy 1: bro, look at that incredibly hot girl!
boy 2: hot damn, but i bet she goes to slutside.
boy 1: so? the girls there are amazing.
boy 2: true, they don't give you STIs either.
A shirt that a slutty girl wears (and wears it more than most of her other sluttly shirts) and is the sluttiest shirt she owns. It could be low cut, see through, spaghetti straps, tube top etc.
It is also the sluts "signature" shirt. So if you see a slut, and your not sure its her, you'll know because its her slutshirt.
"Hey Mikey, theres that hott chick Summer rockin' that shirt she always wears a lot."
"Jim, thats her slutshirt! It makes her tits jiggle to where we can see!"
or
"Hey Cindy, you wear that shirt alot! its super slutty! Stop wearing it!"
"No fucking way! Its my slutshirt!"