When I'm deciding if an online comment is civil and productive, I tend to ask the question, Would the commenter be willing to say this the same way in real life?

Plenty of people use the Internet's cloak of anonymity to say things that are inconsiderate. I use this simple test to determine if they would stand behind their remarks if accountability were in play and anonymity were not a factor.

I think it's well understood that "fuck you" is considered an offensive term in the context of a disagreement between two strangers. My morning commute has illustrated this point on a few occasions. :)

It's possible OP didn't realize what he was proposing would have a negative impact. Rather than assuming that, we could've just said something like: "Do NOT do that! Because of {these things}. And {these other things} will happen to you and other people."

There are plenty of ways to say politically incorrect things without being rude. One thing I like about HN (as opposed to reddit) is the information density -- it's higher because jokes and snark are frowned upon.