Being undermined at work in front of everyone?

This is a little vague. Is it a boss, or a co-worker, and is he getting made fun of, or are his ideas being shot down? If he is getting made fun of, there are laws protecting him from workplace abuse. But if his ideas are being shot down, he will have to talk with the person shooting them down and find ways to improve. And he might want to start looking for a better job. Normally when people are being undermined at work, people think they are not doing a good job and they are on the way out.