How do you react if your wife cooks a dish you don't like?

Do you mean something that didn't taste good,,, in that case it was usually a situation where we would both take a bite, look at each other and simultaneously agree to order a pizza,,,

Or are you referring to her making a dish that she knew perfectly well that I didn't care for but she made it anyway just to piss me off,, in that case I would get up from the table, make myself a sandwich and retire to the other room to watch some television.

I eat it anyway but that very rarely happens.

I be honest with her and tell her to try better next time.

Don't react at all. 

I would never cook fish,

With surprise - I'm not married.

Make her lick it off the floor.