I think there are two kind of people not accepting a simple "No":

1. The assholes.

2. The men who have been taught that sometimes a woman saying "No" means "Perhaps" or "Go on". So they think they need to insist because maybe the woman just want them to show how much they are interested in her.

The problem is that many women actually want men to insist: they complain "I told him 'No' because I wanted to test him, why he's not asking me out anymore?!?".

Until there are women like that around, men will never know when a "No" is really a "No", or it's a "Perhaps, go on asking". Since we are NOT mind readers, there's no way to know in advance.

Maybe we should invent some kind of code: you know, some kind of shirt, cap or badge, saying "My 'No' really means 'No', goodbye". ;-D