"The government shouldn't be in the business of marriage at all, so of course I vote against gay-marriage."
I also like "of course I'm voting 'no', gay-marriage doesn't affect me, so why would I support it?"
I tell the peasants that I'm trolling when I do this just to see their reaction, but the truth is I'm showing that debater how their argument is self-defeating. Some, few, get it and make stronger arguments on facts which stand by themselves. The rest keep a quote of me saying 'I'm a troll' handy when they need an 'easy button' out of a conversation.