Ian has a very valid point; basically take lemons and make lemonade. Take the opportunity to turn it into something positive, at least as a point to learn something. It is frustrating to have someone belittle you, and is hurtful too. Why does he do it? What could you be doing that brings it out in him? What can you learn from this?
Another suggestion too; maybe this fellow doesn't have a good grasp of etiquette and the sempai/kohai relationship. Even if he is technically better (and this is a big IF), the relationship dictates respect (respect goes both ways, you as sempai should respect the junior for his potential and to nurture him; he as kohai should respect you for your experience and time on the mat). Possibly a good sit down and talk would help alleviate the situation.
Anyway, just my $.02