Howdy! Here you can share all those embarrassing/hilarious things that took you a liiiiitle too long to figure out. Don’t know what I mean? I’ll start!
I was 25 when I realized that TGIF stood for Thank God It’s Friday.
I was earlier this year year’s old when I realized the word “towpath” is in fact “towpath” because of towing things, and not “toe path” as in…you walk on it with your toes I guess? IDK. I’m dumb.
GO!
I was thirty-something when I realized a guy in high school had had a crush on me for most of the school year. He said nothing about it, but at one point his friends asked me to prom on his behalf while he had his face buried in his arms on his desk (the edge of his forehead was bright red though). I already had a date unfortunately who I wasn’t super into, if I could go back in time I’d go with him! He was a nice guy! We also would not have been a good long term couple so it’s not like this is a life changing thing at all.
But yeah. Sitting in traffic on the way home over a decade later and I realized that it was more than just that one event of his friends giving him a hard time, there were other clues from months prior. Doh.
It was like… last year I found out it was “can’t be assed/arsed” not “can’t be asked.”
When my husband makes pizza, I can put olives on my half. And then I’m guaranteed to get my leftovers because he doesn’t like olives! I went years without keeping any olives in the house because he doesn’t like them and we normally eat the same thing, but I now have my very own jar of olives that I can add to whatever I feel like.
Oh gosh, I feel like I have a million of these…but of course I can’t think of most of them right now 
One I do remember: only two years ago I realized that the phrase “pulling out all the stops” refers to playing the organ- when you pull out all the stops on the organ, it makes a big honkin’ loud sound. So, you’re going all out.
I am a musician. I played organ for 8 years. It should not have taken me 28 years to realize this lolololol
That’s one I didn’t know! Awesome!
Trying to think of some, drawing a blank for now. I’m sure I’ll think of some later!
Heckin SAME.
I’m sure I’ll come up with some good doozies as I think back. I’ve had so many “you know how old I was when I learned X thing? I was TODAY YEARS OLD.”
My husband has a ton of these though, since his family really isn’t good at idioms and the like. Here’s a few I remember being “ahas” for him.
“Sheep in woof’s clothing” —> sheep in wolfs clothing
“It’s a mute point” —> it’s a moot point
“Woof it down” —> wolf it down
I love eggcorns so much.
I had never heard that term! TIL.
My mom and I also collect ones our family messes up for medical terms. My favorites there: “hen flew end ways” for “influenza” and “speetle-ma-Jesus” for “spinal meningitis”
On that note, this came across my fbook feed yesterday.
I was late teens when I discovered the “bells on bobtails” in Jingle Bells referred to bells on horses, not the local lizards that Europeans didn’t know about when writing the song. In my defence, lots of bobtails around my house and no horses.
This reminds me, my husband just found out this Christmas, when he asked me what the fuck “reindeer paws” were, that the song goes,
“Up on the housetop, reindeer PAUSE.”
WHAT!!
But…reindeer paws!! 
Well, I was today years old when I realized that!
But reindeer have split toe/hooves they’re related to deer. (Blanking on the normal words for those… they’re both even toed ungulates lol. Is hooves the word I’m looking for? 
)
I’ve always heard it called a hoof. Just a split hoof or a two-toed hoof.
Haha. I mean…I know reindeer have hooves in real life…I just thought Santa’s reindeer in the song had paws because…well it just always sounded like it in the song 
You’ve got one up on my BIL. He apparently thought reindeer were made up animals like unicorns. He also through narwhals were made up
I remembered one of mine! I love the song “Dangerous” by Big Data. Heard it tons of time. Just the other day I realized the line “They been watching all my windows” is meant as word play for the OS. I always just thought of house windows 
I thought for way too long that Donatella Versace was someone SNL made up.
This:
I learned this last year aged 35. I personally blame my parents for either not knowing this or not teaching me this.
I can do calculus but can’t keep my foil in its box.