That´s up to you, but there isn´t a rule that you have to be dominant 24/7. For example when you go out with friends you don´t have to behave in a certain way, because you don´t play dominant as a role that´s the type of person who you are. So this means you don´t behave in a certain way because it´s expected of you, you behave in a certain way because that´s who you are!
If people don´t like your behaviour then that´s too bad, because you don´t have to pretend to be someone you´re not! But it´s not a bad thing to keep the dominant side a bit under control, as much as you feel like whipping your friends I doubt that most of them wouldn´t really appreciate that. But being dominant isn´t restricted to wielding a whip. I doubt that being dominant is put into just a couple of words, there are so many ways of expressing yourself and we all have our own ways of doing that. Besides there isn´t always a need to express yourself with dominant behaviour, a Dom/Domme likes to relax as well every now and then!
Some people do expect a lot from a Dom/Domme, which then sometimes leads to disappointment for this person because Doms/Dommes are people too and don´t always live up to certain ideas. As a Dom/Domme there is very little you can do about that, because when someone steps into a session with certain expectations then there is a good chance that he or she will be disappointed. Don´t try to live up to certain expectations, do what you always do and what works for you. Of course it´s not a bad thing to break the routine, that keeps things interesting.
Could you pick a Dom/Domme from a group of people? Maybe some people can, it´s not like a Dom/Domme has a sign on his or her head but body language can say a lot and social behaviour can say even more about a person. It´s the trick to pick up on that, while certain things are quite obvious other things can be easily overlooked if you don´t know what to look for. That doesn´t mean you should behave differently around people that don´t know about your life as a Dom/Domme. Even when they don´t know about your Dom/Domme side they probably know you as a dominant person, it doesn´t have to mean anything to them and things start to get suspecious when you suddenly behave differently. Just be yourself!