Women scratch the shit out of us too y'know. I've had blood on my shoulderblades before. But hey it's whatever you're into. Some people run with this type of aggression and think it's hot/kinky, but it's wasted on some and definitely not appreciated by others.
I think biting/scratching are fantastic, but it does have to be done in the heat of a passionate moment (not just out of the blue). I would think, however, that a gentle bite or scratch would be made as a way to see how your partner reacts...then ask them what they think, or do it again, just a tiny bit harder, and look for a reaction on their face or in their eyes.
There is nothing less attractive to me than a man who is unable to lose himself in the moment when we're having sex. If losing yourself in the moment means a few hickeys, bites or scratches for me, then so be it! I will gladly bear them. :wink: