So I said that today, without thinking, because I don't think I'd heard anyone say that in oh, 10 years or so and I don't know how or why it would've slipped from my mouth, because I don't know anyone named Maynard, and I was in fact talking to my friend Tony about this unbelievable Strawberry and Lime chewing gum I had and I looked at him in shock and thought, "Wow, I wonder where that saying came from."
Well, hold on to your britches, because you (all 2 of you that read this) will be very happy to know that it came from a commercial in the 80's, where a father gets his kid to eat his food by telling his kid's imaginary friend, "Good stuff, Maynard."
And there you have it. Has your day improved? Mine has, because it was something that would've killed me had it not been for the wonder that is google.
I wonder where "hold on to your britches" came from.