Sayings and idioms I didn't understand until very recently

"Floor so clean you could eat off of it". This might not be my fault, because I was raised in a household where this was never the case. I thought this meant you could eat off of a plate that was set on the floor, instead of a plate set on the table. It wasn't until a year ago that I realized they meant like food straight up served on the floor. 

"You can't have your cake and eat it too". So this one always seemed nonsensical. Why are we talking about cake? But I understood that it meant "you don't always get what you want", I just sort of didn't know why. Then I saw an Instagram reel about it like a week ago. If you have a cake, and eat it, then you no longer have it. You literally can't have it and eat it at the same time. However, the way it's phrased doesn't imply this at all. One can have a cake and then proceed to eat it too. 

"Double-edged sword". So this one, I've always understood the meaning. A blade that hurts the wielder, as well as the opponent. But all swords are fucking double edged you nonce. It's not like a knife, where one side is blunt. Both sides are sharp. I'd get it if the pommel or handle were also a blade. But that's not what we're talking about here. So this one is just straight up stupid.

Honourable mention: "The world is your oyster". I use this one all the time. It comes from Shakespeare. In its original context, he says, "and I will crack it open with my sword" or something to that effect. I don't like that. I like the absurd notion of the word being an oyster. Not just any oyster. It's YOUR oyster. And you can just go ham cause it's your oyster, and there may be a pearl or there may not be, but either way, you're getting some oyster.