I can't get over how funny it is to see someone in a huge lecture hall raise their hand, get ignored by the professor, and slowwwlly bring it back down in defeat. Gets me every time. Gotta give 'em credit for wanting to say something, though. If I ever have a question that's good enough to ask, I'm going to keep my hand raised as high as possible until I'm noticed. Maybe even yell out the professor's name, depending on how important it is. But considering the fact that I'm usually overwhelmed by the amount of information being thrown at me and the fast rate at which it's being thrown, I'll probably never have time to think up a good one until the professor's already moved on to another topic. I guess my only option is to inwardly chuckle at the poor, brilliant chaps whose eagerness to participate in the lecture is repaid with utter rejection.
I'd like to note that it's the general situation I find amusing, not the sadness of the individual involved. So if this has ever happened to you, I'm laughing WITH you, not AT you.