The details are that TTYs in general on any *nix are a huge mess with lots of complicated interactions and weird historical behavior that doesn't make sense. The linux tty stack for a long time was a huge clusterfuck. Now thanks to Alan it's just a normal clusterfuck. That's the context for this incident, which basically happened like this...
Some dudes: there's a bug in the ttys
Alan: ok lets fix it
Some dudes: here's a patch
Alan: that patch breaks a dozen other things
Some dudes, Alan reject a bunch of solutions
Alan: we can fix it with a hack, but it breaks emacs. Emacs is relying on unspecified behavior, so it can go suck an egg.
Linus: well it SHOULD (sic) work like this, and emacs is too holy to break. This problem is easy, are you a retard?
Alan: look we can hack it and break emacs, or do a huge rewrite
Linus: hacks suck, linux should be awesome in every way. Also, your code smells
Alan: it's going to take forever to get this right
Linus: then revert the patch that introduced the bug
Alan: that patch was applied years ago and removing it would break a dozen other things. You didn't think I'd think of that? Who's the tty maintainer anyway, jackass?!
Linus: I don't like your attitude
Alan: Then fuck off I quit!
Linus: Oh yeah did I mention your code smells?
Linus: and let me quote you something you said earlier, so I can show what a bad attitude you have.
The TTY and serial line code is basically a huge Rube Goldberg machine and Linus was telling Alan to tweak something somewhere in the middle of this huge contraption. Having followed the TTY code a fair bit, I totally side with Alan on this. It's a miracle that it even works, and not something you can just stick your head in and give advice about how to fix. Also, if Linus is so concerned about proper behavior for user space programs maybe he should take a look at ioctl... because it's completely screwed up in linux.