What's the worst possible reason to vote?

My wife has just voted in her first election here since getting her citizenship, and she based her vote on (get this!) the party with no chance of winning! You think you know someone... Anyway, this leads me to wonder what could be the worst reason someone can have to vote?
Of course, I'm also open to the possibility that there aren't any [b]bad[/b] reasons to vote. As long as you vote, no matter the reason, even a racial one, you've done your civic duty.