Wild Thing by Josh Bazell
If you possess delicate sensibilities......don't pick up this book, or the previous book of Bazell's, Beat the Reaper. Violence, vulgar language, sexual tension (but no real sex!), and funny as anything I've read. Not overtly funny, but deeply, cynically funny. Warped humor even. Just my brand of funny.
Interesting premise of a young man deep into the mob at an extremely early age, and for many good reasons turns against them. He enters the Witness Protection Program, goes to medical school, becomes a doctor, and then has to flee (again)for his life. All of that is in the first book. In this one he is in yet another incarnation of the Program and becomes involved in a Big Foot/Loch Ness/monster problem.
There has to be another sequel.....the ending is wide open for it!