I guess most pax don't realise that the cabin crew are the ones who are ultimately responsible for the security of the plane - and our lives depend on it! The gate-staff aren't going to be flying with any potential security-threats or be the ones to sort out why there aren't enough seats for the passengers. So to grumpy SLF, give us a break, we are doing our jobs for our and your safety. Keep your boarding pass in your hand so you don't get all flustered trying to find it in your oversized hand-luggage.
The number of times we catch passengers at the door who are trying to board the wrong plane is frightening.