Soooo you’ve heard two people having a conversation and you want to add your comment, should you?.. probably not. If all you are going to do is validate one of the statements or opinions already said then don’t. And don’t get your feelings hurt if the two people in the conversation don’t care to entertain your comment. If you have some additional information to add… for example if the conversation is something technical and you have experience AND a solution then sure, chime in. If all you are going to so is say “yeah I’ve had that very same problem with my radio.. i have no idea how to fix it” then DON’T. This isn’t fakebook and you are not “entitled” to join in on a conversation between two people just because YOU want to.
So.. in short… if you have something beneficial and positive to add then go ahead, if you’re just joining in to be “part of the group” then don’t.