To cruelly laugh in the presence of someone's misfortune.
I got fired today and my boss's assistant nelsoned me as I was cleaning out my desk.
I fell while rollerblading in the park and some jerk gave me a Nelson out a car window.
(Verb)
To lose all human control and revert back to one's simian roots. Usually resulting from seeing an attractive woman or, if you are a comic book fan, a mint copy of The Avengers #1.
Did you see that girl at the club that I was talking to last night? I was really chimping for her.
Mark looked at the woman and began to chimp heavily.