I guess I'm an odd bird here, because I love helping people, when I can. If I don't know, of course, I stay I don't know. But if I do know and it's not interrupting the instructor talking I am happy to help someone near me figure something out. I tend to learn quickly, though, so it's not usually a burden for me to spend MY class time helping someone.
I get stuck, sometimes, even in the craft store. I must have an approachable face or something; it is rare I can get in and out of a craft store without being asked for help or advice on something. 99% of the time I'm more than happy to help; it's rare that someone takes advantage and badgers me when I am in a rush or something.
I end up training people at work all the time, too, even though that's not my job. Maybe I missed my calling and should have gone into teaching!