What's your relationship dealbreaker?

I was reading this great post one of my girls over at The Frisky wrote about how she was fantasizing about this guy she used to date, then she noticed how he had posted all this "Global warming is a myth" nonsense on his Facebook profile. And just like that--poof!--all her love for this man dissipated into our already (truly) strained atmosphere.

But all this chatter got me wondering: What is it about someone's behavior or beliefs that can sour an otherwise perfectly promising relationship? Is it the man who's a soldier, and you're too afraid he'll be deployed? The staunch Republican to your Democrat--or even the Hillary supporter versus Obama? The hot guy who also happens to be a Scientologist (or worse, one of those Landmark weirdos), and he's always trying to recruit your friends?

Or could it simply be the person who once broke your heart so bad you could never forgive them enough to give it another go? So tell us, what's your ultimate relationship deal breaker?