A wave where people in a crowd throw their hands in the air (and often rubbish) in a consecutive manner moving around a stadium. Often seen at cricket and rugby games. Sometimes when the game is really exciting (or boring).
Hey look Ford, there's a hell mexican wave happening.
The act of nodding one's head at a friend or aquintance instead of the traditional wave.
Katy: Why does Steve never wave at me when I wave at him?
Maria: He did, look at his head, see he gave you a mexican wave.