Tacky, tacky, tacky. I am betting that the only reason anyone gave him $20 was because that was the only bill they had in their wallets and they were too stunned to try to make change.
I also HATE any service where you pay for a ticket and no mention is made anywhere of tips. Not on the website, not when you buy a ticket, nowhere. But at the end they brazenly ask for tips. And I am not talking about dinners, I expect to tip servers when I go out to dinner. I'm talking about other events where there are employees, presumably making more than $2.17 per hour, but at the end of the "event", someone gets on a mic and says please tip our wonderful employees if you enjoyed this event and they have someone holding a hat on the way out, so everyone can see if you do or you don't. I hate that. Just tell me the REAL cost of the event UPFRONT. I will pay it or not go, but don't spring it on me like that. I also don't carry cash, ever.
Once I was invited to a "chocolate and movie" night at a friend's house. It was a cute idea, and there was some chocolate fondue and fruit/cake to dip. And a large prominent jar with a "contributions for chocolate" note on it. Really? If you can't afford to host people for dessert only, you really shouldn't be hosting. I am totally ok with "let's all chip in" on any event as long as it's upfront and everyone wants to do it. But don't pretend to host only to play broke later. Don't make me feel guilty for not bringing money for chocolate, I had no way of knowing it would be something you would expect money for.