Overreacting because someone doesn’t know something can make them feel crappy, embarrassed, like they’re missing out or stupid. It will make them more reluctant to talk about certain things with you.

Person 1 - I love movie name it’s a classic. Person 2 - I’ve never seen it Person 1 - Omg, how haven’t you seen it!?

Instead go with - I’d really recommend watching it, I think you’d like it. It’s about…

Or

Person 1 - Did you see person in the news Person 2 - Who’s that? Person 1 - Seriously, you haven’t heard of person

Instead go with - they are… they were in the news because of…

Doing this will build trust and a feeling of safety if they just don’t know things. They are also more likely to watch/listen/read etc the thing, and then come and talk to you about it afterwards too.