What did Malack do that made Nale hate him so much?

[Keltest]

No one but possibly Rich knows or likely will know, barring a Linear Guild/Vector Legion prequel, which is a possibility.

Generally, people's speculations fall in one of two categories: "Something seriously horrible, because Malack was seriously horrible" or "Something laughably petty, because Nale was laughably petty."

I have a hard time imagining "Something seriously horrible, because Nale was laughably petty."

Ok, that's not true, I just have a hard time not laughing at the idea.

"Malack probably killed a person and made Nale bury the body or something. That's totally the kind of thing Nale would get mad at him for."