When my dog (an English Cocker Spaniel, for what its worth) is behind some glass (e.g. a glass door or a car window) and someone taps on the glass, even just a little bit, she gets into a fit of rage. She has always been treated quite well, so I can't imagine what causes her to behave like this.
The first thing that came to my mind is that she perceives whoever is tapping the glass as teasing her, and she feels disrespected, or something like that. This sounds far fetched, but could there be any merit to this theory? If not, what else would cause her to do this?
I believe we know that monkeys interpret teasing correctly (I don't know this for a fact). That is, they know when they are being teased and they (correctly) interpret it as being disrespected. Could the same thing be true for less intelligent animals like dogs?