Agreed. If he wanted to talk about the problems associated with jobs based on tipping, or why the minimum wage isn't high enough, or any number of other issues

Agreed. If he wanted to talk about the problems associated with jobs based on tipping, or why the minimum wage isn't high enough, or any number of other issues related to the US service economy I would definitely be sympathetic, but when you earn tips at work, you don't get to complain that the tips your received were inadequate (except perhaps to your coworkers). You do not publicly question customers about their tip generosity in any public forum if you intend to stay employed, let alone Twitter. I worked in food service jobs for years, yes I know the money is bad and the work sucks, but the solution to that is getting a better job not shaming your customers and embarrassing your boss.