It's a metaphor for the wearer (person) that has the big sad and needs mental support because they are probably gay. They often feel like they are left out or lonely and tend to listen to sad and depressing music.

This is because slippers often look as if they are sloping or saggy we associate that they're sad or depressed.

((CREDIT TO KALLIE FOR FOUNDER OF THIS PHRASE.))

A term used to reference cannabis/marijuana/weed.