Or
B) Get impatient, cut them off and tell them everything you know about the topic?
Or
C) Patiently let them finish, THEN tell them you already know, and everything you know about the topic?
I personally have a tendency to be an impatient douche sometimes so I admit I don’t always handle these situations with the greatest patience & social grace.
Honestly, it kind of depends how well you know this person and what kind of relationship you have, but I think it’s best to take the “Yes, and…” approach.
If you like or care about this person, then definitely don’t rudely interrupt them to shut them down by telling them that you already know what they’re saying. Obviously you don’t have to pretend like you don’t know… But people want to feel like what they’re saying matters, so give them the small win of hearing them out, and then affirm them and add something to what they’re saying of you can.
So, here’s an example of what you probably shouldn’t do:
A: “So the other day I was watching a video on painting and I found out that if you mix blue and yellow you–”
B: “Green. You get green. I know that. I know everything about mixing colors. Everybody knows that.”
What would be better in most cases, would probably be something like.
A: “So the other day I was watching a video on painting and I found out that if you mix blue and yellow you get green. And mixing blue with red will give you purple.”
B: “Yeah, totally! And red and yellow gives your orange, right? And I’ve heard it’s also a good idea to have warm and cool versions of all of the primaries, so that you can get more mixing varieties.”
So, you’re both listening and affirming what the other person is saying, and then demonstrating that you know a bit about this too by adding to it. You’re not making A feel useless, stupid or unappreciated. You’re not making yourself look like a rude jerk or a know-it-all.
Obviously it depends heavily on who you’re talking to and what your relationship is. (Some people who are friends love to talk shit to each other for fun, and in that kind of relationship you probably don’t need to be as careful about hurting the other person’s feelings.)
Generally speaking, though, it’s good to remember that a conversation isn’t just about you exchanging information with another person, and so it’s important to consider how other people feel when you talk to them, in my opinion.
I read two sentences of that and figured I already knew the rest.
I figure you don’t.
I let you finish!
This is similar to the guidelines for correcting someone politely. Like if you used a word wrong, instead of saying well actually that word means this, you use the word correctly, you can affirm what they just said but using the word correctly. So you never directly correct them.
It’s the same basic kind of principle.