The papers today suggest that the announcement: “You must stay in your cabin and class of service”, is not actually an airline rule! However if you breach instructions and ,heaven forbid, push back the curtain or use the business class toilets, yikes, staff might strong arm you. Suggestions here:
1. Get all names of staff involved. If they say they will contact the captain write down his/her name as well. Be discreet.
2. Record witnesses’ statements on your phone.
3. Send a certified letter to the airline asking for an apology- they will not compensate you so just go for the apology then tell the world.
DO NOT make a fuss while in the air or you risk serious, if unfair, consequences.

The so called Contract of Carriage on each ticket is your actual legal contract with the airline. Before you book with a new airline , read this contract of carriage.