Pot Blocked
When you head to your favorite bathroom stall, only to find it in use by someone else.
When my morning coffee hit, I ran to my favorite bathroom stall, only to find myself pot blocked by some asshole.
Pot Block
When one is about to smoke some pot and something happens to keep you from doing so.
Johnny was just about to light his joint when his mom walked into his room with the DEA. What a pot block.