This is slang for weed that is between schwag and chronic in quality. This weed is also known as 50, because it is $50 per quarter, which is where 5th Wheel derived from.
"I can't fuck with that reggie, that shit makes my head hurt. Get at me when you get some 5th Wheel."
the 5th wheel is the spare wheel attatched to the back of a slab. the 5th completes the slab. without it you are not ridin slab. it can often be seen in a tilted or "reclined" position.
In a group of friends, the one friend that is kept there as a backup, they do just enough to keep him/her around. Only to to stuff with when the usual crowd of friends can't. Like the spare tire on the back of your car.
Scott: Crap I've got 3 tickets and only Jake and Connor can go, Tanner said he couldn't go. I guess I'll have to see if Luke can go instead since we've got no one else.
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.