Funnier than sh*t

I was talking to a friend the other day and during the conversation, one of the things she said was "....is funnier than sh*t!!!"
How does this phrase make any sense? How is sh*t really funny that something could be funnier than it? I never realized that sh*t could be so funny. Then again, I guess it is.
It's wonderful that we can debase ourselves to such lowly forms of humor, even as "adults".