1. A poorly rolled blunt
Like a taco the contents of the blunt are spilling out and/or loosely packed making it fairly messy.
2. Any blunt thats considered whack
-aka taco for short
Brian, Mikey, and Travis are about to smoke so Travis rolls a blunt. Travis sparks it and passes it to Brian.
Mikey takes a hit...
Mikey - "Dude what the hell, i just got bud in my mouth."
Travis - "Whatever man, its straight, the papers were just a little stale"
Mikey passes the blunt to Brian and it completely unravels..
Brian - "What the fuck son, all i got here is this blunt taco"