My college professor teaching FLUID POWER tried to teach our whole class that air does not compress and liquids do.

When he started the lecture and I attempted to correct him in a very soft and kind way (thinking he obviously is mixing up words) he denied it and told me I was wrong.

I tried several times to correct him nicely (because there were people in the class that would have taken his word) and was met by more and more aggressive denial. I finally stood up in the middle of the class, threw my hands up and said "Well Fuck! I just wasted all this money on a new air compressor" and walked out.