I always find it funny (and slightly embarrassing when it happens to me) when I hear someone use a popular saying, but it's been wrong. Close, but wrong. It makes me think of the etimology of sayings, and if people knew where they actually came from they could understand the saying, instead of just repeating it because it suits the conversation.
Two I have heard somewhat recently:
"Nip it in the butt." This made me laugh, and think of someone being nipped in the butt with pruning shears, ha ha. Obviously the correct term is "nip it in the bud" - referring to cutting the bud off a stem before it becomes a flower and takes the nutrients away from the main flowers. Or in that context, to stop something from happening before it becomes a big deal.
The other is "nerve wrecked." I actually got into an argument with my "friend" (and I use the term loosely) whom is ALWAYS right and will research research research on Dr. Google to prove you wrong. I tried to explain that it was actually "nerve WRACKED", as in wracking one's nerves, but she wouldn't have it.
This also brings me to think of when lyrics are misheard on songs. I tend to make my own lyrics up as I deem fit, ha ha, so I'm a big violator of this one. (I should give myself the nickname "The Violator" and come up with an awesome made up lyric theme song for whenever I walk into the room. But that would probably give some people the wrong idea.) I don't have any examples of this one, but I know I've done it before. Feel free to give me some examples.
And one of my favorite, things you should have known by now that you didn't realize until recently. My radio station has listeners call in with this one and it never fails to crack me up. One of the examples is this: We have a heavy population of Hmong immigrants in this area. One girl saw a sign that has a picture of a couple of people and underneath that it simply said "XING". She assumed that it meant that was a Hmong neighborhood. Now obviously this sign simply means a pedestrian crossing. I couldn't stop laughing and told my Hmong bestie as soon as I got into work. Another was that a girl thought there were stop signs in the sky to control air traffic. She literally thought that is what air traffic controller meant. Sometimes you just have to shake your head and laugh.
I can't think of any for me personally, though I know there have been some recently where I just stopped and though, oh, duh, that makes TOTAL sense!
Feel free to add you own! I promise I won't laugh (too hard.)