How's it hangin is a polite greeting from one man to another. "It", in the context, is the man's penis. Presumably if it's hanging well, the man is doing well.
by RexGibson April 26, 2004
How's it hangin' is a very informal way to say hello to your fellow. What is actually hanging, is evident from the following example.
by KAO1 November 02, 2005