This is the Best Advice. A thick skin is a vital skill, and not just for the Internet.
It took me many years to finally stumble on this epiphany. Being offended or hurt by something sucks, whether it's unintentionally or just because someone else is being mean. It sounds tacky, but in the end, the only person who controls whether you're hurt or offended by something is you. You have this power, and no one else.
Call me whatever nasty things you want. I don't care. :)
Yes but.
The bane of the internet, to me, is this notion that "Oh, just develop a thicker skin, you'll be fine". You do need to ignore assholes, but that's not a zero-effort solution.
One person in a day calls you shit? Fine, that's easy to ignore. Ten people? Not that hard, but it starts to get at you. One hundred? One thousand? More? And if you've had a hard day, hard week, hard month, hard year? If you're already dealing with all these other stresses, all these other problems that you're trying to manage, and then you start getting more crap thrown at you?
When I write something to another person online, something I try to remind myself is that I can't see their face. I can't stop talking if it looks like they're getting pissed off, because what I wrote is already in their face. I don't know what else is going on in their life. I don't know what other people are saying to them. I don't know how thick their skin is right now, in the end.
All I can know and control are the words on my screen. I've got no need to piss someone off, I've got no desire to make someone's day harder. So I'll pull my punches whenever I can.
I mean, why hurt them? That's what RP characters are for!