It's just his Chaser persona, i watched a program he did about trying to cut out sugar, he was on for quite a few weeks and he always came across as a really nice guy.
I've never seen the programme but, upon looking up info about the guy, I see that his degree is in Mathematics and that he taught the subject at secondary level for 15 years. As those statements also apply to me, I can understand exactly how life has made him turn out a bit 'odd' ;-)