In my girlfriend's family, we refer to oversized old comfy pajama-esque stuff as your "complaining clothes". (One of them said it as a kid and it stuck.)
This is a great and useful term and I want to spread it, because there really isn't a proper succinct descriptor for these clothes otherwise and there needs to be.
@V complaining clothes? I don't quite get it but I like the term regardless! :D
@Nine I think the idea was it's the clothes you wear when you're laying around complaining that you feel kinda gross and won't go to work today, etc.