Why parents can be so embarrassing

Watching an acquaintance try to control his mom's behavior this weekend made me think a little bit about why we can be so easily embarrassed when our parents mix with our friends, especially when we live far away from our hometowns and the majority of those who know us now didn't know us as children or adolescents.
But then it made so much sense. It isn't just the ways that parents can act silly and do things that we don't want to think of them doing. For instance, a man in his mid-twenties might not want to see how his mom acts when she's drunk--because to him that's his mom, not a complete person with all her faults. And he might not want to watch his dad hit on women half his age, for the same reason. And, a man in his mid-thirties (like me) might blush a little when his mom decides to tell stories about what he was like as a child or what he thought "you hurt my feelings" meant when he was four. You mean my feelings aren't in my butt?
The real thing that embarrasses us, I think, is the way that they uncover our inauthenticity. The majority of people I spend time with, who know me, didn't know me when I was a child or a teenager or even before I was thirty. That means that I have a had a fairly free hand in creating a "me" for them to know. I get to be the author of my own identity, as if I were some sort of autonomous Ayn Rand character. But, when Mom shows up, she tells the lie. Because, after all, there is another "me", one that existed before, one that she knows, one that she had a hand in creating--not just biologically, but socially and psychologically--and that can be a lot like being stripped naked in front of strangers, since it really is stripping off the mask that I have created for myself. So that's why parents shame us; and it's also why it's so good to be embarrassed by them. They remind us who we really are, at least what parts of us are.