I know how difficult it can be to find time to have a snack especially if you have break or lunchtime detentions to do. Your line manager seems to forget that you are not one of the pupils and have hardly grievioulsy transgressed! As for standing up to bullies; this must be done! I was shouted at in a public area by my HoD because I had asked a pupil not to shout out "Oh my G..d" because I was a Christian and found it offensive. The boy had continued to say this and I had given him a detention. I asked my HoD not to shout and said I would take up the matter with the headteacher. At that point, she quickly backed down but I went to see him anyway. He backed me up and she was given a verbal warning. I was on long-term supply and even though I don't think she forgave me for this, she certainly never spoke to me in that tone of voice again. Always try to stay calm and speak to the bully in a serious and controlled manner; don't stoop to their level.