I must say, it's increasingly evident in this thread that a small number of cabin crew let that little bit of authority go straight to the head.
Yes, cabin crew are trained in door operation and evacuation procedures. It's also fairly easy to work out - you generally pull the handle in the direction of the arrow and the slide inflates automatically. Now being SEP trained gives me a quicker reaction time of course, as it's been drilled into me, but it's not like the door will not open unless it's a cabin crew member doing it.
Safety is the highest priority in our job. Everything we do revolves around it but it must be remembered that customer service is the most visible part of the job. Being cabin crew is not some higher calling, it's a job - a job that has immeasurable impact on how customers view your company.
There's an influx of immature crew coming online now in almost every airline, who think it's ok to "tell off" a customer. I reserve this for the most serious of cases. For minor things, a polite reminder of company policy and safety regulations is all that is needed. No need to establish yourself as the "safety police".