Yes, how dare you ask questions about sexual technique to potential clients in a co-ed forum on a hooker review board! Next thing you know, someone's going to start a thread about why dudes like strip clubs -- it's a slippery slope.
Guys like it all, really. One guy I knew liked me to bite his base as hard as I could until he exhaled while he counted out my bites (luckily I never broke skin). We made it up to over 30 once before he blew his load. A fwb of mine awarded me an invalid Nobel Peace Prize for my tip work, whereas most dudes jump out of their skin and cry "mercy!" at the same moves. Some require a hand while others consider it cheating. I watch a lot of blowie porn simply for technique ideas and I'm constantly learning new tricks to try on certain participants.
All that being said, I have known a few boys that love nibbles. Nibbles on the boys, at the base, tugging at their foreskin, and along their ridge for the daring. And yes, I'm talking teeth.