I kind of see your point, although my first impulse would have been to punch the guy, but then I would be charged with assault. It’s a screwed up world. Well, I would not want that thing waving in my face if I were here so “engaging” him would be the only way to get him to stop, because the other passengers were not willing to help. Would be a shame if my little “assisted opening” Browning knife were to brush past his privates, with all the jostling on the subway and everything.
The young woman was very lucky this guy wasn’t more dangerous. You have to have a screw loose to act like that.