Here are a few nice ones, I can’t really pick:

“Capitalism is the extraordinary belief that the nastiest of men for the nastiest of motives will somehow work together for the benefit of all.” - John Maynard Keynes

(You can also apply this one to proprietary software vs. Free software (don’t say open source in my presence))

“The tyrants are only great because we are on our knees.” - Étienne de La Boétie “Those who do not move, do not notice their chains.” - Rosa Luxemburg

don’t say [those words] in my presence

Will I regret asking why?

Not OP, but I personally heavily dislike the confusion surrounding those terms that’s entirely self-inflicted. “Open-source” referring to FOSS as a whole, and what open-source sounds like actually being called “source available”, is needlessly confusing.

I usually write FOSS since I like acronyms, but when I speak I’d say open-source. I don’t see how open-source is any more confusing than free software, considering most people would immediately think “free as in beer”.