Like when you send a .7z instead of a .zip or .rar to a friend or a teacher because that's what your computer has installed and they're like "Oh No, not one of those, now I have to install 7Zip" even though the same program that opens .rar also opens .7z I feel like people are way more annoyed when they receive a .7z
I did that once. They didn't even notice. Really bummed me out. To be fair, it was after I had them install 7Zip, so the fault is mine. Haha