Yes, flash mobs have a bad name here (in Philly), after they started mugging people and damaging property. We now have a curfew for teens. 9 pm. Out of center city and west philly.
Flash mobs need to have a positive purpose. They can’t be just for the sake of a mob. A mob will always find something to do, and if it isn’t guided right, it will turn violent.
Why do you want to form a mob? Just to do it? I hope not. I hope that you will pick a purpose of doing something good for the community—something good that is needed at this moment in time. See if you can organize a mob around that.
At the very least, let it be an artistic flash mob. It could be an art happening of some kind. But please don’t let it be a violent thing.