Flash Mobs: The Power of Mass Engagement
No symmetry
If it is way to obvious and has too few people to create a stage for themselves.
Unrehearsed. If you're going to do it, do it right.
Not many people and at a party for instance as it can ruin it instead of making it fun.
A flash mob that fails to meat my criteria for a good flash mob, i.e. a flash mob which purpose is solely entertainment.
few people involved
when it is bad organized, not many other people sees it, when it has offensive content, when somebody's hurt etc
boring coreography and / or music
One that drags on.
I havent seen a bad flashmob. I guess a low amount of people, asyncronous motions between Them, an empty location