free puff

The smell of cannabis hanging in the air when someone else smoking it passes by

Just got another free puff.
Did you smell the free puff.
Lots of free puffs around here.

gap filler

A behaviour that is conducted to avoid awkwardness when there is no one talking. It can be a useless sentence or an unnatural smile etc.

A: Oh the weather is nice.
B: Was that just a gap filler?