To block someone from hitting more marijuana, usually mid-rotation on a piece or bleezy or spliff. Similiar to a cockblock.
Potblock scenario
Ronald was about to take his hit
Zackary says, "No I think you have had enough man." and sticks his hand in front of the piece, blunt, spliff.
When you get blocked by an extremely hotindividual from doing something you want.
Susan: I want to go lay out by the pool but there are two athletic girls out there showing off their bikini body's.
Spencer: You just got hotblocked girlfriend!
Susan: What's that?
Spencer: It's like getting cockblocked but the pool is like the person you want and the hot girls are like a big cock.