I know it was lame to ditch to party to watch Sex and the City, but I needed some 'me' time. I knew I could trust you not to tell anybody; I'd never hear the end of it! Thanks for undermanding, bro.
Underman, or undermensch, is the opposite of Nietzsche's 'Uberman', or overman. Underman is what manwill devolve into, and will assume a state close to that of a feces-flinging chimp.
John: Did you see the Henderson kid? He can't do anything but drool and suck applesauce.
Jack: This is what happens when paternal twins marry: they produce the underman.