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.
I usually let them finish, Even if I already know about whatever they’re dumping onto me, unless it’s something that I don’t feel super comfortable with. I’m obviously not gonna listen to a long chat about insect facts, but will listen to someone chat about why they love something like Summer Camp Island, a show I’ve seen every episode of multiple times over.