I really don't understand why this is so difficult for anyone to understand - if someone says no, it means no. It doesn't mean you just try carrying it on with them. IMO, if you do try and carry it on with someone, they do have every right to go to the police.
I once had someone (we were out with a group of friends and I didn't know him - he's now a really close friend) approach me in a pub. Being well aware of what his intentions were, (he was clearly trying to make conversation, nothing more) I couldn't whinge something about harassment or whatever. But it was clear from what he was saying and doing, that wasn't the case at all.