currently im a brown belt in karate but i have a few fellow student that could possibly be the worst.
he is a higher ranked brown belt. everytime he comes to class he always fake strikes a vital organ and says, "boom, i broke your neck" or something similar. also, at one point he told another brown belt that he had placed hidden cameras throughout his house and was spying on him. he is also the type that is very concerned with being the best and beating people during sparring. he always leeches off of others, drinking their drinks, eating their food, 'borrowing' money, never offering anything in return. he also has to know about everything that anyone else talks about and gets mad if we do not tell him. on top of that he responds harshly to criticism.
other than that, theres probably around 20 more things wrong with him that i can think of, but he works hard (not smart), has decent physical ability, and is loyal to our GM.