Term derived from slang. Normally used in England. I mean you'd sound like a bit of a nob if you used this in America or something.
Anyway, basically it translates to "What's up? You're extremely attractive" It is now mostly used by teenagers who are wannabe gangsters (like I stated earlier) or a group of guys saying it as a joke.
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.