This word does not need a definition. It doesn't make sense, it's just funny. USe it in any situation (E.g. uncomfortable, awkward, happy, sad, excited, etc.)
Mate 1: "What should I wear today?"
Mate 2: "Ya mumsskin"
Pajama casual is a term used when working from home and preparing for a video conference. All business above the waist and your pajama pants down below.
We have a Zoom meeting in a few minutes and I’ll probably go pajama casual.