Jean Grey would make the world's most difficult girlfriend. You could never lie to her for one thing. She'd just read your mind. Women already have a natural intuition. Believe me, they know when you're lying. Jean Grey's psychic abilities take it to a whole other level. "Do I look fat in this?" / "Girl, why do you even ask?" She'd tell you that she'd never use her powers on you, but you just can't trust that. Keep the dark thoughts away.
There's alo the fact that she becomes the Phoenix, a psycho god-like creature. Men and women both have their moments of being crazy, unfortunately women also have to deal with getting their period as well. I can't imagine how men would deal with being flooded with hormones, but that's a different topic. Now compound all of that crazy with being possessed by the Phoenix. You couldn't win a single argument.