Let me tell you something about Hew-mons

They can't speak English though. In fact the scene this screenshot is from is them trapped in the past unable to communicate because their universal translators are offline. I would assume Quark speaks Federation Standard, but apparently that's not close enough to English to figure out what they're saying in the 40s

I would assume Quark speaks Federation Standard

I assume he made a clear point of never learning it.

I'd put larger odds on Nog and Rom eventually learning it (but not at the time of the screenshot).
- I could see Quark learning it. He lives in the federation, and fluency is good for business. Probably a RoA to that effect.
One thing I've always wondered, and this is hardly the most unbelievable aspect of the science fiction elements of this show but it's one of the most pervasive and constant; why don't we ever hear the native languages of the aliens underneath the sounds of the universal translators? Most, although not all, of them speak by vibrating the air, so where are those sounds disappearing to?
- The translator also emits an interference pattern that cancels out the original speech to the listener
- This was a plotpoint in DS9 where the UT didn't picked up the nuances of a language but the mutants who were able to comprehend the language deciphered what was really meant.
- They actually do this in Star Trek Beyond
Quark would never lower himself to speaking anything human. He views humans and the Federation as inferior and foolish.
- Understanding a customer as famously wily as the Federation through language would be a business advantage. We know this because it works today.

They're able to say it. It's an insult.

I read a theory once that "daimon", the Ferengi title for captain, could translate to "good/lead merchant" or something along those lines.

So if we assume that's true, it's possible that "hewmon" means something like "shitty merchant", and it's just pure coincidence it basically sounds like human.
- I like this theory, it feels like one of the authentic ways that slurs in earth languages actually get invented.
- Ahh yes, the Monkeigh defense. I always knew the Ferengi were really space elves!
Human is the one word they know in Federation Standard. They go out of their way to mispronounce it.
That's what I figured
- I mean it is usually said with some distain in the voice. I had always thought it was some sort of pun or something.

My headcanon is that most of their speech is ferengi being translated by the universal translator, but when they say the word human they just use the human word for human which then goes untranslated.

Makes sense considering we know from Darmok that the universal translator doesn't translate proper names.
It's not even head cannon, this screenshot is legit not just from the episode, but from the scene where there's an example of exactly what you described.

Quark can say human, he's just unwilling to do so. He makes it into an insult instead.

I love how your legit using a screenshot from a scene where this is explained lol.

Still less absurd than Data's contractions (except all the times he actually used them). Maybe it was something he was programmed to tell humans so that even being superior to them, people would still be able to point to one thing they could do better.