Sometimes being very popular among the common people can be very frustrating. You just don't get the privacy you desire. Boy wonder Justin Bieber actually felt this way when he was waiting for his girl friend Selena Gomez at the Toronto Airport. So when some fans came up to him to ask for an autograph, the Biebs was not happy at all.
I personally don't think he was being rude or mean but just trying to make them understand. Like he said he had a long day and was tired. Anyways he actually took pics with them once Selena got there.