Hey ho - how did we know that was meant to be light-hearted? Not in joke thread, was it, and the word 'stupid' is offensive to many, if we don't know the context. Now I am glad to hear it was in jest ... as you know so well, us teachers try very hard to use that word with children. It can be difficult on a Forum to know what the intention of a post and use of some words was.
So nothing to do with sense of humour at all. Some of us to pick up accents like sponges - I had a huge Stoke accent after working in a local engineering firm for a while ... so I can understand how his accent has changed in daily contact with the French- and that it does NOT make him stupid as such (even if he is a nasty man - which I have no idea about - even so, it would have nothing about his accent though, would it).