Ah, I've just realised that this is the one who sent us a whiny, entitled email about the warning, and then when he didn't get a response in a nanosecond followed it with a '?' type one. When we pointed out that this did little to disprove the attitude posted about above he quickly switched to the obsequious smarm (I don't know whether we replied after that because I haven't looked).
I doubt he's dangerous, but if his email is anything to go by he's likely to be a monumental pain in the arse in the room, and also to sulk like a petulant toddler if he doesn't get his own way or if you disagree with him about pretty much anything. Whether or not you take a booking from him depends a lot on your tolerance for self-obsessed man babies, but you'd need a lot more than I have.
He also apparently believes that he's the only 30's Asian man in London who goes to a gym (in which case it must be mine because I saw an Asian man in my morning HIIT class), so he's either as dumb as a rock or he genuinely thinks that the universe revolves around him. My guess is a bit of both.