People who do not understand how their machine operates or how to do the basics like dropping feed dogs, changing tension, even changing feet. I was at a FMQ class and two of the six were almost completely unfamiliar with their machines. The instructor spent most of her time helping them cope. The class was not cheap and I really felt like I did not get my money's worth. (But it might have been the instructor too. She knew most of the other students personally, and I felt very much the 'outsider')