This can have two meanings. One is simply and FINALLY getting to having sex with someone you have wanted to for some time after overcoming many obstacles. The other meaning is rating the act of the sinslide afterwards.
Willie: I finally got to scoring the sinslide with Rach!
Bronk: Well, from the sounds of it you are stoked to have finally scored the sinslide, but seems like you would have scored the sinslide with a positive rating!
When you wear shorts and a t-shirt indoors (typically in a dorm) when it's really subzero outside during the winter. A concatenation of "stay inside"'s.
"Why are you wearing beach shorts when it's 8 degrees outside?"
"Too lazy to put on pants since I just going downstairs to pick up Chinese delivery, so I've got on my stinsides."