I will just add that on a flight that I operated as Senior Cabin Crew with easyJet, I had 3 positioning crew seated at Row 1 ABC who were sat directly opposite me as I read the safety briefing over the PA.
We had in 1C a Captain, 1B a First Officer and 1A a Senior Cabin Crew Member, throughout the first part of the safety brief they were sat there giggleing then they started talking very loudly and my acidic looks didn't shut them up. So I released the push to talk button on my PA handset and said to them "Excuse me! You three should know better - pay attention or move to another seat!" they looked positively shocked at my response but the passengers seated on rows nearby gave me a thumbs up and nodded in agreement to what I had said.
I continued reading the rest of the safety brief and then started the cabin secure. The SCCM in 1A still had their mobile phone switched on during taxii out (it rung as we were approaching the runway threshold), the First Officer in 1B didn't know how to do up his seat belt and was reaching over his shoulders for the shoulder harness!!! The Captain in 1C sat there in silence looking sheepish because he was feeling embarassed with the fact that his two positioning colleagues had been caught out.
Whilst they were positioning in their civvies I knew they were crew because they made a big fuss during boarding of showing their airside passes and saying "If you need any help in an emergency, let us know!".
Now for the worst part of this story, they were positioning easyJet crew! (I will just add though, the vast majority of crew positioning - be they easyJet or any other airline will at the very least be quiet during the demonstration so that passengers nearby have the opportunity to see and hear what is being demonstrated. The three in my story were the exception to this usual rule).