If I were an instructor, the following things would really annoy me - (they do as a fellow classmate!)
1) being late - and being obnoxious/noticeable/noisy about it - for no good reason -
2) not listening and prattling on and on about something non-relevant
3) thinking his/her way is better - maybe so - but shut up until the class is over!
4) not bringing supplies on the list - the other students may not be thrilled about sharing
5) over-estimating one's ability
6) if class is "too simple" - just hush - might learn something new, anyway
7) sewing machine not capable of doing what is needed for class
8) Being impatient and not waiting until the next step is presented before asking questions