Here's an advanced social skill that you might not be aware of: just because you've thought of something to say about a topic being discussed in your presence, doesn't guarantee that the conversation will be improved by your saying it at that exact moment.
So if somebody you want to talk to makes a statement with which you disagree, you're under no obligation to gainsay them at that time. In fact, unless a negative outcome is imminent as the result of a factual error, it's almost always better to keep your argument to yourself.
That's assuming your goal is a friendly interaction with that person. If what you want to do is stir shit, be a nuisance, look obnoxious, and derail the conversation in progress, then by all means gainsay your little heart out. But expect to get muted at best and at worst shamed.
Disagreeing with someone to their face is rude by default. Disagreeing without insult is an extremely delicate maneuver. That doesn't mean you CAN'T disagree with people—it's a free country or whatever—but what you can't do is feel maligned if it's understood as an opening salvo.
Okay, time for a pop quiz!
1. I tell you I'm making lasagna for dinner. You're not eating at my house or anything, we're just shooting the shit online. You say:
2. An author you like is giving a talk. They mention their favorite book by Donna Tartt is her first, The Little Friend. You know her first was The Secret History. Afterwards there's a Q&A, and you get selected to ask a question. What do you say when you take the mic?
3. Your friend's cat is missing. She calls you in a panic. What do you tell her?
4. I've been hired to paint a mural of my favorite actor, Derek Jacobi. "Derek Jacobi is the best actor who ever lived," I say dreamily as I show you my sketches. How do you respond?
5. Dame Darcy is making me a cake for my birthday. She's raw vegan so the cake is made of dates and green apples, which you're pretty sure I can't eat because I have that thing where raw apples make my mouth swell up. Do you tell her to consider a different cake?
6. A cartoonist/twitter personality you enjoy, who does not follow you back, writes a series of thoughtful tweets followed by a quiz designed to gently help her very least favorite people on Earth to be happier and less annoying. You think might've spotted an error in it. Do you