By all means, I love when a man pulls my hair back and makes me scream out "MORE".  But when does it become to much? When he has a fist full of hair and I'm rubbing my head in pain. I understand pleasure and pain falls hand and hand. But, in the heat of the moment, there can be too much pain. And as the old saying goes,"Too much of something can be a bad thing".
What do you think?

It's too much when the one receiving the pain determines it's too much.  As with anything else, communication is essential with this kind of play.  Would it be as much fun if the person was too gentle?  Don't make me guess, tell me!