Imagine a character so completely depraved, degenerated and perverted that he makes Hannibal Lecter seem like a Sunday school teacher. Now imagine that character fueled by a mountain of cocaine and an ocean of vodka. Now take away any sensitivity he may have learned for others of a different race, gender, physical capability, social class, postal code or sexual preference. Make him believe that there is nothing so important as the pursuit of money, put him in a nice suit, give him an expense account and turn him loose on the world without a modicum of care about the consequences of his actions to himself or others.
Now if I told you that you were going to read a novel centered on such a character, you might expect it to be a horror novel, or a thriller, maybe a mystery or police procedural. You would probably not expect that it would be the funniest thing you've read in years.
I will caution you here: if you don't think humor can possibly mix with buckets of blood, vomit, urine, feces and semen, or if you couldn't possibly laugh where there is blatant bigotry, or if wretched excess offends you to the point where you lose your sense of humor, this might not be the book for you.
If, however, you're possessed of a strong stomach and aren't easily offended, you're in for a treat.