Anyone who defines the word munchkin as anything except an internet insult for someone who has a differn't style or taste in roleplaying than someone else, is quite frankly, and quite factually, wrong. This is one of those rare instances where I know I am correct.
How?
Simple, interview 100 people on what they think a 'munchkin' is, and you will get a bunch of differn't opinions. Oh sure some may agree with each other, but that doesn't make it the correct definition.
The fact of the matter is, a lot of people use the word to insult someone elses game. They may try to justify it by saying that so-and-so is bending the rules or powergaming or what have you, but that doesn't make it any less of an insult.
That being said, I can assure you Lord Ravinous, that the only way you can be a 'Munchkin' is if you decide you want to be one. There is no clear cut list of qualifications.
K Koie