Why do most attractive women have a really nasty personality ?

Based on my life experience with attractive women, I see no basis for your claim. To the contrary, I find almost all women, & the attractive ones in particular, to have very pleasant personalities. Maybe you should look inward & find if your perception is skewed for some reason, or if there's something about the way you approach them that inspires a negative reaction to you.

Because having looks doesn't necessarily equate to having class or showing much decorum

I had a similar experience before. Some attractive women tend to think just because a man talks to them in a platonic fashion that they want to bang or make a girlfriend. It's best to just take them down a few notches. The narcissism is quite appalling.

I give em three chances. If they are still snooty after that, then they are gone for good. I might make an exception if I know someone is ill or something.

Sounds like an appropriate response, to me ...unless she was some sort of toilet tour guide.

ask men in future