First, I'm going to make a few guesses: that you're in high school, you're American, and that the general population of your school consists of 'regular people'-- ie, they are considered to be normal in our dysfunctional society.

You probably get these 'looks of utter bewilderment' and the occasional giggle because you caught them completely off guard. If they are 'normal' people then they look at you with a sense of bewilderment because they are so suprised that anyone could do that. It is not 'normal' to give oneself a compliment and it either scares or confuses them, probably both. That, or they think you're some sort of egomaniac who loves oneself.