Deep down... (or not so deep down?) John IS a nice guy. He's a professional and is good at his job and isn't going to pick fights in the middle of the precinct. (He just fits the antagonist role for the evos easily). But he IS weary of evos and probably doesn't like the possibility of his mind being read at all. That's his private stuff in there- if he wants someone to know something, he'll say it.
Haha and I know it is impossible to ask Corin to hold back.