A greebo is, typically, a massive, fat, sweaty, long haired mess. Greebos are not necessarily fat, however, although they are usually sweaty messes. The typical greebo is into heavy metal and likes to use the word 'awesome' regularly, un-ironically. The current definitions on 'urban dictionary' for the word 'greebo' were almost 100% written by greebos. The typical greebo enjoys hanging around metropolitan town centres in a cult-like crowd, asking their friends "where their hugs are". They then attend greebo nightclubs, for example: the Glasgow Cathouse, and end up "sooooo drunk :3 xD" before leaving and infecting the local fast food outlets with their drunk greebo patter. Do not be surprised if you see a greebo wearing a metallica or iron maiden t-shirt, because this is the norm for them, and do not be surprised if you see them in public and cringe. It happens.
Rab: do you see that filthy greebo over there?
Josh: aye man, fuckin boggin.