I had a fellow student in Goju one time that was a real joy to work with. He was a big guy (6" 4-5" 210lbs at least) with an even bigger attitude. He was a prison guard and approached people the same way he did the inmates. Always in your space, very intence, and tried to intimidate everyone he worked with. If you had to do a drill with him there was never any give, he would just push people around and tell them their technique would never work on him. Wrist locks, arm locks were a nightmare to learn for most people when working with him. I learned that by introducing him to what I now know as an atemi waza it made him much more agreeable to a lock technique (re-knee to the thigh, thumb to the arm pitt then apply the lock-very hard) Suprisingly enough his reaction (once released) was to smile and tell me how much he liked working with me because I wasn't afraid to mix it up like some people in the class.
It takes all kinds.