Every once in a while you come across someone whose ignorance on a certain subject is just mind-blowing. Like these ones:

What was your "Wtf, how do people NOT know this?" moment? from AskReddit

Ready to cringe? Here we go. Thanks, Reddit.

1. Clean your cleaner.

You need to clean out the lint trap in a dryer.

I frequently come across people in their 30s that can’t figure out why their clothes take so long to dry…

– edging_but_with_poop

2. The shape of things.

My aunt once argued with me that H2O was was not two parts hydrogen, one part oxygen, but a word on its own—maybe spelled Aitchtwooh? I was never clear on that.

“It’s just another word for water it doesn’t stand for anything.” I was 13. I still get mad remembering it.

– maiafinch

3. Basic astronomy.

An insane amount of people don’t know and absolutely refuse to believe that the Sun is a star.

– sarabichat

4. Shifts in time.

Went to a middle school where the teachers did the “group well-performing students with students still having some struggles” approach and I had to sit next to a total *sshole for half a year (not because he was having trouble with grades, there’s no shame there, he was just also an *sshole) but the thing that really hit me was that he just refused to accept the concept of time zones. Thought I was making them up.

I even showed him a time zone map that came with our d*mn calculator and he was like a Westworld bot just unable to receive the information of this magical world in which he’s lived all along.

– Dangercakes13

5. What’s up?

I heard a guy once complain that the suppositories he was given were so big he had to cut them in half to take them.

– SantiagoandtheMarlin

6. Not how fractions work.

I was in a small town (i.e. tiny town — not even a traffic light) convenience store. The candy bars were marked 3 for $1.00. I picked up two and headed toward the checkout. This store did not have an automated cash register, just a drawer.

At the cash register, the cashier said, “Those are 3 for a dollar.”

I said, “That’s OK. I only want two.”

Cue disturbed look on his face. “I’m going to have to charge you extra.”

“OK,” I replied.

He thought for a moment, then with a look of pride he said, “50 cents!”

“OK,” I replied, before racing out of town with my 16.6666 cents of ill-gotten gain.

– ThatGuyFromOhio

7. Just browsing.

“Ok…what exactly is a browser?”

-An actual ticket I received.

Edit: I work in IT and a browser is a web browser in this context.

– theGuyInIT

8. Sex ed.

I once made out with a girl, nothing else.

The next day she called me, crying asking if she could be pregnant.

We were both 22.

– discostud1515

9. You know we can hear you right?

When I watch the actual criminal investigation shows on the CI channel:

The suspects who betray themselves in the interrogation room when they think they are alone and there is no camera and microphone.

– princedudesert91

10. Half and half?

I had two separate adults, in one week, not know that 0.5 is the same as half.

– three_left_socks

11. Classy classification.

Someone told me that Whales were Fish Not mammals and even after googling it he still thought it was a fish.

we were doing a project on a mammal of our choice and i suggested A Blue Whale

– Digitydoggimmeahigh5

12. Maps are confusing.

Saw someone with an Alaska plate while on vacation in Tennessee, told my mom it must have been a long drive for them to get here. She responds, “LOL son you can’t drive here from Alaska it’s an island!”

The 4 other family members in the car agreed with her, and I just had to sit there realizing everyone I was with was dumb as sh*t. I was around 13 at the time.

– superdonkey23

13. Yikes.

Had to explain to a 20-something year-old what the Holocaust and who Hitler was

– nyetizen

14. Very eggciting.

I dated a girl once who could not get her head around that I know how to poach an egg at home.

– Douglasqqq

15. You’re toast.

While growing up, I caught my intellectually gifted sibling sticking a metal knife into an active toaster to get bread out early

– P0tat0_Carl

Well. Live and learn, I suppose.

What’s something that took YOU way too long to learn?

Tell us in the comments.