Originally posted by Steve
Why should you train with him? Are you an adult? Are you paying money to learn aikido? This guy is your sensei's problem, not yours. You could try this: Next time simply stand next to a pair of people who are practicing and wait patiently. When your sensei asks what you're doing, tell him, "I won't practice with So-and-So." If he asks why, tell him.
I've seen people do that kind of thing before, with the effect of dividing and almost destroying the dojo. IMO, the people that make you the most uncomfortable are the people that you should be training with the most.