Now and then you get some jerk who challenges everything you say, monopolizes every discussion, and just won't shut up and let you take control. They ask all kinds of questions that are outside the scope of the class outline. What is it with these morons, anyway?
Think for a minute. How did you feel the last time somebody in authority "suggested" that you attend some training session that was number 226 on your list of priorities? How did you feel sitting in the classroom? Like a kid being made to finish your broccoli? How did you behave? Like a mature adult, faking enthusiasm and overflowing with empathy for the instructor? Baloney! If you're anything like me, the circumstances made it real easy for your inner jerk to rise up and take over.
That jerk who is giving you a hard time may be the most conscientious person in the class. He or she may be acutely aware that they are wasting their time, and they don't like it. They would rather be doing something productive. They're frustrated, and they take it out on the only target in sight - YOU.
So what to do? I don't have any surefire solutions, but for starters, avoid a contest of wills. You'll lose. Try empathy. Acknowledge privately that you realize the person would rather be somewhere else, and that you aren't offended. Ask, again privately, if there is anything you can do to help. Even if there isn't, you may at least develop some rapport that will relieve the tension.