Don't use sarcasm on the internet (or at least not on HN), it usually ends with a bunch of responses which didn't pick up on the fact that it was sarcasm which lowers the quality of the conversation. Remember also that many HN readers are not native english speakers and are unlikely to pick up on the true meaning of a comment if you're not really clear. Even suffixes like /s are not clear IMHO (at least, I didn't know what it meant until I saw the other comment here suggesting it and I AM a native english speaker).

Jokes and such are frowned upon on HN and many people probably see sarcasm the same way, so you risk getting downvoted too.

In order to avoid adding noise (in the form of responses from people who didn't realise you weren't serious), I would suggest to refrain from sarcastic comments.

I will definitely cease using a useful rhetorical device in case a handful of people might misunderstand me.

A trailing /s is the convention. Failing that, perhaps less subtlety? Text is poor at conveying tone.

Why don't I put a flashing red sign that says I am joking while I'm at it?

It's up to you; you're the one controlling the chances people will get the joke in your comment :P.

At this point I'm resigned to people taking even the most improbable interpretation of whatever I say if it gives them an opportunity to call me an idiot.

Much to my occasional regret, the principle of charity is far more often invoked here than adhered to.

Unfortunately, HN doesn't support blink tags.

Where can I make a feature request?

I thought it was pretty obvious and the italics made it more so.

People can be very wrong on the internet so it's hard to tell sometimes.

Also, Poe's Law. https://en.wikipedia.org/wiki/Poe%27s_law