How to act during your ident for castings - in character, or as yourself
It depends on what kind of persona you wish to portray! If you're really nervous and it shows, then maybe you should put on a bit of a character! If you're really bubbly/happy/friendly, then that's good! But you also run the risk of being overly happy and coming across as desperate/weird!
The main goal is to be friendly, polite, happy to be there and show that you're willing and easy to get along with - this is especially important as people are going to have to spend hours on a set with you when you get the job! It's not advisable, as yourself or a character, to walk into the room like you own the place and start moaning about the wait! They know! They've been in that stuffy room all day as well and now they immediately don't like you, even if your audition was better than the last person - he was a nicer guy!
Idents are recorded on camera - they're there for these casting directors/producers to remember and assess later. The footage will be passed to their boss and probably their boss and further up the chain - whatever you do will be recorded for everyone to see, forever. This probably isn't the best way to go viral!
Any extra time you can get with the casting director or producer etc at an audition is valuable. Except if you're miserable, then you hope they forget you very very quickly. It's all time that gives them more chance of remembering you, so don't waste it by looking bored or being miserable because there wont be any small talk and you'll be straight out. Don't forget to be polite and friendly to everyone you meet - the person who greeted you at the desk could well be the producer, or the casting director's son/cousin/niece/wife/neighbour! Whoever they are, they have more say than you at that moment and they could easily let people know if you're rude to them. Overall, it's best to aim for the main points above. If you have to put on a character to do that, then great! If that's your natural self, then great!.