1. An Insult e.g Your a bag of wank
2. Something very crap e.g My computer is a bag of wank
3. A bag that jumps down the street in a jerking motion (The original term came from when people watched bags blowing down the streets when they were bored they used to say "This is wank" shortly followed by "Well thats a bag of wank" at that point the person saying the phrase would then point at the bag.
What a bag of wank or this coffee tastes like a bag of wank