Hi Linda:
I think you're right, and in one way, humor just about anytime is a welcome change from lectures, work exercises, or busy activities. We want to make sure we're serious about our instructional delivery, but that doen't mean we can't have fun we're at it. The key is that it's appropriate humor, provided in moderation, tasteful, and if we can relate it to the topic or work setting, all the better.
Regards, Barry