What’s common sense to one person is rocket science to another. And when you encounter someone who has absolutely zero clue about something so obvious, it’s easy to think they’re just a complete idiot. Sure, you don’t say that to their face—but you CAN say that to Reddit.

In a recent post on the social media platform, people sounded off about the top moments wen they realized they were surrounded by idiots. Here are our favorites.

1. What Tax Is

   “I used to work at Walmart as a cashier. During tax free weekend, the place was a mad house. The lines were long and the customers are non-stop. That being said, I can say that at least 80 percent of customers would point out to me, quite angrily, that their total was still including the tax. For example, if their purchase was 148.67 they would wonder why the tax of .67 was on there and why it wasn’t an even total, like 148.00 even. I had to repeatedly explain that’s not what tax is.”

2. Why Donate Blood

   “A girl I know once asked why anyone would donate blood. She said that you only got a certain amount for your entire life and giving it away didn’t make sense.”

3. The Double Pacific

   “First day of college, girl raises her hand and asks why there are two pacific oceans on the map.”

4. Finding Your Phone

   “My friend once couldn’t find his iPhone in his house, so he rang it from the landline. His iPhone rang, on the table in front of him, he picked it up and obviously, there was nobody on the other line. Screams upstairs to his parents, with a phone in each hand: ‘Who is ringing me?’ I sat there facepalming.”

5. Halloween’s Date

   “I had to explain that Halloween, in fact, can never be on Friday the 13th.”

6. Where Rain Comes From

   “I once had an argument that rain was “new water” bestowed to us by the Earth. My friend truly believed that water did not recycle, and the consuming it meant that it never saw the Earth again. Also believed that anything flushed down a toilet or drained was burned and evaporated into nothingness.”

7. The Human Breed

   “Just yesterday I had to explain to 3 coworkers that humans are animals…”

8. The Male Anatomy

   “My sister had some friends over, one of her female friends dropped: ‘Do men have an anus?'”

9. Blueberries Aren’t Real

   “I met an American woman travelling that got aggressive trying to convince me that blueberry was a flavor and not “a real thing” while obsessively picking out all the little blue/purple ’round things’ from her blueberry ice cream.”

10. The Moon and Sun

    “I tried to explain that the moon and sun were not the same size, then all of a sudden found myself having to explain that the sun and the moon were in fact Different and not just one side fire one side rock. They all laughed at my crazy theories, then asked if the sun was so far away, why is it in the same sky during the day (on earth) as the moon was at night. They pissed themselves laughing, and I just laughed with them.”

11. Telling Time

    “My sophomore year of high school when I found out 80% of my class couldn’t read an analog clock.”

12. An Air Cadet

    “Girl walks into music class and tells everyone that her history teacher called her an air cadet, but she didn’t know what he meant by this. He had called her a space cadet…”

13. What Time the Sun Rises

    “I’m in a meeting with my boss, the Director of Corporate Sales, and the Marketing Manager. They are confused as to what time the sun rises in Ireland (we are in the Boston area). I tell them that the sun rises in the east and sets in the west, so countries that are further east see the sun first and therefore Ireland would be in the afternoon when we were just seeing the morning sun. They didn’t believe me. It was a 30 minute conversation where despite my best efforts to discuss how the earth moves around the sun I couldn’t convince them. I still work in the same office with the same people.”

What’s an idiotic moment you witnessed with someone?