I don't think sarcasm is going to do much. It's just going to show people that you don't care too much about righting a wrong. Heck you might just be provoking them. Call me crazy but I have a few ideas.
1. Put together an informational site on Wicca including anything and everything that you know about it. When you finished and you make it look all pretty, perhaps trying spreading the word around for people to go on the site. I don't know how you'll pull off that one. Be creative. Maybe you'll get a few supporters, maybe not. Either way, you tried.
2. If people start picking on you and asking questions, answer them as honestly and politely as possible. For example: An idiot walks up to you and asks, "Next time you sacrifice an animal, can I come along?" You reply, "Sorry, but I don't sacrifice animals. Wicca is all about being in harmony with nature and its surroundings." Yes, it's a stupid example. Work with me here. Tweak it a bit.
3. Ignore it. And before you roll your eyes at me, just listen. There will come times (yes, it's plural) in your life where there will be nothing you can do except ignore the ignorant *******s. Eventually (and hopefully), they'll get tired of knawing on the same bone and go find fresh meat.
Perhaps not the best ideas, but you'll never know if they work until you tried. Best wishes and blessed be.