Your boss will likely look down on you more than him if you rat him out. At work my policy is to do my own job and get paid, let the rest be damned. People who get involved in office politics, especially when they drag me into it, really piss me off. Talking to the boss behind peoples backs like you are asking about is the one that gets me the most.
Why don't you be a man and ask him why he hasn't done anything all day long?
Why don't you be a man and ask him why he hasn't done anything all day long?