"Nobody's perfect," my mother always said. Who made her the authority?
I objected to her uncharacteristically brand bromide when I was a kid—and four decades later, I think I've finally articulated why.
"Nobody's perfect" assumes that everyone—or the speaker, at least—has a settled notion of what human perfection is. It implies that the only problem is that everybody's striving for it and everybody's falling short.
That, in my experience, is just as untrue as it is dull—almost perfectly so.