A few years ago, we had one girl, a former karate student, that joined our beginners group. After a few classes she insisted that she want's to practice with advanced group (the group I'm in), and one of the instructors allowed it.
During one of the advanced classes she was in, she began acting like she already knows everything better than the rest of us do (after maybe 2 months of practice). On one occasion during one technique I resisted her technique on purpose, and of course her technique didn't work. Then I did a kaeshi waza and pinned her to the ground with sankyo, not twisting or yanking her hand, but just holding it so she can't move; she was frantically trying to get herself free (she even tried to hit me with her legs). After that "lesson" she didn't want to speak with me for the rest of that class, and in fact i think she never came to class again...