I have seen rugby fans behaving inappropriately and have also been in friendly situations with opposing football fans similar to those that you describe. I can think of my trips to Portsmouth and West Ham off the top of my head as being two examples when I have been in the heart of opposing territory and still had a great drink and craic with the fans.

I think if there is a tendency for rugby fans/players to be more gentlemanly (and at university level I know this is definitely NOT the case) then I think it may have more to do with the nature of the games themselves. In rugby, the best team generally wins. However, in football, because it is so low scoring, injustices regarding who wins a match happen more regularly and this may lead to issues.