I read somewhere that Bush made this awkward figure of speech not because he didn't know the idiom, but because he realized too late that he'd be saying "shame on me" on air, which is apparently a phrase absolutely Verboten by political media advisors (because it could have been taken out of context and used by his adversaries). In a way that says a lot about the political culture that resulted in a figure like Trump, I think.

Seems like the better option is to simply say, "you know the rest of the saying".

Perhaps he actually just flubbed. Many such cases.