Logical fallacies. If you plan to participate in any sort of serious discussion, whether that be about politics with a rival for public office or breastfeeding with your mother in law, learning about logical fallacies will only be to your benefit. They don’t teach this in schools, unfortunately. (maybe in debate, I dont know.)
One very common fallacy is the ad hominem.
An ad hominem involves attacking the person, not the argument.
I actually couldn’t get the page I wanted to link to to load, so I’m settling for Wikipedia… However, wikipedia has a nice pyramid diagram showing an ad hominem to be better only than mere name calling, lol. (name calling: “well, you’re mean and dumb.” Ad hominem: “but you don’t even have a college degree.”)
If an ad hominem (or, worse, name calling) is your first reaction to being disagreed with, that says something interesting about you as a person. (I mean, more than occasionally – we all have those 6 year old “yeah, well you eat boogers” moments.)
But if you stick with that long enough to write it out and share it with others… That’s just lazy thinking. That’s admitting you don’t have a leg to stand on. Or, it’s inadvertently (or purposely) using faulty thinking and poor reasoning. You shoot yourself in the foot, as you’re making your own argument or position invalid.
You put yourself in a much stronger position when you avoid logical fallacies!
Also, as this website points out, logical fallacies are often used by ads and politicians. Learning the basics of logical fallacies helps you to see through their crap. That’s always good.
(note: not a scholar of logic. The study of logic appeals to me, but I’ve only dabbled. However, learning some basics of logical fallacies a long while back helped improve both my writing and my speaking – as well as my thinking.)