As usual, this sort of question is phrased about you being concerned about someone that your other half is friends with, when in fact the issue can only ever be about your other half, and not their friend. Why? Because they can be as 'laddish' as they like and can try to hit on your girlfriend as much as he wants, but nothing will happen unless she wants it to. My wife has been hit on by plenty of guys in the time we've been together, and been friends with a couple who tried it on with her as well, but nothing happened because she was never interested. And equally, I've never been concerned about that, because I trust my wife, and always have. So no, you shouldn't be concerned about this guy or your girlfriend's friendship with him. If you trust her, it shouldn't be an issue.