I agree, it's fun to crack a hard crook mentally.
I love punching on with them (five years of boxing, thai, freestyle karate and bjj plus seven years of Army) but there is nothing more fun than taking a hard crook who's got some one hundred charges or so to their name into the interview room when they have a smug grin on their face thinking that they know it all and then in a calm voice, without threats simply using your noggin making them wish they had never been born as they change their storey six times on an interview tape before they snap and suddenly don't want to say anything more. I sometimes struggle not to laugh.
Cheers
Dave