Just to offer a man's perspective, this natural phenomenon is nothing to be embarassed or self-conscious about. As a previous poster said, any man with any real sexual experience will have come across this before, so he won't be startled or put off.
To be honest, in my experience it's always been the girl who was more suprised when it happened. It seems that quite often it's the woman who is unprepared and unexperienced with this phenomenon.
Take care...