Seems like the best thing to do when being heckled would be to play along. Have fun with them. If you're confident and proud of your craft, you know that for these few hecklers there are probably still people in the crowd that enjoy what you're doing, and you need to play for those people. Who knows, maybe if you kill the hecklers with kindness or a good dose of humor after the show they might slightly change their opinion of your band. I'm sure they'd still think the music sucked, but they might have a tinge or regret for disrespecting some genuinely cool dudes, even if the music sucked balls.
If I were playing the show and I noticed some dudes playing Uno on the stage, I'd call for a couple beers between songs and set them down next to their cards so they could at least have a nice beverage during their uno game until we got off stage. Maybe even spit-free!