How do I politely reject =xxx?

In my experience one of the first rules in dating is honesty. That doesn't mean being unkind or uncalled for in your comments or actions. However it does mean telling the truth when required. So, if you're not interested in someone you don't necessarily have to give an in depth explanation, but a simple 'Thanks, but no thanks.' is usually fine. I think comments such as 'ewww' and so on are just childish. However when you are using dating sites you will come across all sorts!