It could be true. You may not be aware of it, but you could be sending signals to your server that you won't be tipping well when the check comes. As a general rule, businesspeople get crisper, more professional service.
Tourists receive more relaxed and verbose service.
Romantic couples are pretty much left alone. An appropriate tip is 15 percent to 20 percent of your total bill. Yes, we know you, you cheapskate. You're the one who leaves the 10 percent tip, apparently thinking that the others in your group will make up the difference. Okay, let's be fair here.