Burn one
From Wiki Weed
The phrase to 'burn one' means to smoke some weed, usually meaning to smoke only one joint or one bowl. You might be most tempted to 'burn one' during a lunch break at work, or during an intermission at a theater. It's almost always a very quick smoke session, so you can get right back to whatever you were doing beforehand — even if it's just sitting on your couch. You can also say you're going to 'burn one down' — if you're not with a bunch of narcs, they will probably know you're talking about weed and not your neighbor's house.