I would also have supported that action, but that's not near as funny.
That would've been the right way to take a stand though, if that's what they were going to do.
Gays accept everything this country has to offer and then demand that everyone accept their lifestyle so the couple's action was appropriate payback. Also there is no such thing as a "slur" against gays, that's like saying you can "slur" thieves. "Fag" and "queer" are taunts which need to be mainstreamed to fight the communist infiltration of America, which seeks to marginalize all those who support the family unit by creating forbidden so-called "slurs" against those who undermine the family unit. Also the person probably wouldn't want to have anything to do with religious people no matter how nice they were to him so at least this way they can make a statement.
Maybe it's because I am coming from a Christian mindset but my philosophy is that to win someone over to your way of looking at things the best way is to set a good example and to show kindness when possible.
Look at these two scenarios:
1. "Thank you for your excellent service tonight. I've enclosed a tip. I may be wrong but I got the impression that you might be part of the homosexual lifestyle. While I can not tell another adult what to do with their life, my personal beliefs based on the Bible are that such a lifestyle can lead to serious spiritual consequences. I wish the best for people and would not want these consquences to affect you. If you would like to learn more about this then here are some resources where you can learn more *list of resources*
2. You did a great job on serving us tonight but I'm still not going to tip you because you're a dirty fag. You are going to hell and I hate you. By the way did I mention you're a fag?
Which one would be more likely to give a positive result? Not that the first one is all that likely to produce an immediate positive result either, but it at least respects the server as a person.