I don't do anything. I'm the kind to completely forget about it minutes after I close whatever I was looking at. If it's a stupid enough thing that made me angry enough, sometimes I'll vent about it to my wife, and usually get the response of "Why do you care what a random person online you'll never meet thinks?" but I've gotten that response enough for it to have really sunk in to the point where I really don't care 99% of the time. I don't really debate online anymore either for that reason. The most I might do is nudge somebody in the right direction if I suspect their opinion is simply based on a lack of information, but if that fails I tend to just delete my reply and move on so I'm not bothered by it again.