Why is there same sex revulsion?

The thought of sexual activity with the same sex can bring a feeling of disgust and dislike as one considers another to have something incompatible on a sensory or nervous level (eww, gay).  Is there a name for this reaction, like an automatic skin or muscle reaction?  Are there any studies on its exact mechanisms? 

it's called sexual orientation, heard of it?  It's the same reaction you get when you see an ugly example of the gender you're attracted to.