A greebo is generally anybody who is different. They usually get abuse hurlled at them because of this by chavs/townies/arrogant twats. I am called a greebo/emo because i wear the clothes i want to listen to the music i want to and generally dont give a shit about fitting in with the crowds. People who labbel others and in effect bully them are usually scared of what others think of them so they try to fit in and make everybody laugh at someone else. Most greebos/greebs listen to some form of rock music or something not mainstream, are peaceful people and dont start fights for the hell of it and are just being themselves.
all of these examples happened to me or friends.
sitting in a maths class and getting things thrown at me because i am "greeb" by a group of guys who everybody is scared of because the could kick the shit out of them.
walking down an path at lunch time out of school when a group of year 9 chavs/townies/popular kids thought a group of year 10 greebs said "they could have them" so made two of them get down on their kness and say sorry. the greebos not wanting to fight did this and walked away whilst having things thrown at them and threats yelled at them.
Standing in the courtyard at breaktime where most of the school are. Generally the big groups of greebs stand on one side and big group of chavs townies on the other and the other people spread out between in little groups. when the chavs etc start to throw any food the have at the greebs this happens nearly every day.
a fat kid taking the piss out of you nearly the whole way through the day about skate boards, music, being greasey and dirty just so the "cool kids" are to busy laughing at the greebs to pick on the fat kid.