This word was created by Barney Hobbs, who attends King Edward's school, Birmingham. He is a bit of a juamster himself. The word does not have much meaning, but it usually used to insult someone, but it can also be a very friendly gesture.
It is usually used instead of the term Wanker, as some may find it very offensive.
There is a theory that this word has been passed down from generation to generation, and has now eventually ended in the mischievous hands of Barney. However, it is a very useful word and can be used on many occasions.
Oh you Crazyy Juamster