Metro (aka Subway).
A couple goes into a crowded train, close to the end of the wagon, on the corner. Later a girl enters the train and moves directly between the two of them, blocking the way.
The train is packed, so it could be seen as unavoidable. The girl blocking the couple does not moves to much, but lingers over the female member of the couple. Both start thinking that something is going on but still are not really sure.
Anyway, the first girl, suspicious of the girl interposed between them, try to keep the grip on her handbag solid, however she think to feel something estrange as the other girl makes a controlled move around her.
Alarmed she start to check her handbag, but as suspected, the purse is gone. Just on that moment the train stops on the next station, the people start moving, including the estrange girl, who just before leaving point to the ground of the subway where the purse lies.
Obviously, the money was gone, with the girl, but at least the cards (IDs and bank) where left behind.
Total time of the action, less than 30 seconds.
Be aware. They are faster than you can think and they are in every subway system of the big cities.