My personal pet-peeve is not so much forum specific but a side-effect of using chats/texts/forums for conversations. One cannot tell tone very much. I get that. I understand that it's hard to understand the tone of what someone is saying. That's why we have emojis and /s and all that to help fill in the gasps that body language or a voice used to fill.
However, sometimes misunderstandings happen.
The issue is that after the person has specified what they meant, or that they were being sarcastic, or even apologetic, there are others who will still keep hammering on that misunderstanding.
Over.
And Over.
AND OVER AGAIN.
To where the discussion is...completely derailed and then feelings are hurt and everything is a mess.
That annoys me.
I'm also admittedly in my thirtys and over the whole "Be positive ALL the time" deal. Life is hard. Shit happens. It's okay to recognize it. It's okay to mention it. It's OKAY to disagree. When folks get really uptight because someone is not joining the kumbaya circle, I admittedly get...a little annoyed. People are allowed to critique, to mention what is missing. IT'S OKAY TO WANT THINGS TO BE BETTER.