While this may at first seem like a good thing, whose to say we won't get some disgusting stuff in there. Call me a sicko for even thinking this, but the possibilities are scary.
I disagree. I mean, some of the romance flirts might be considered a little racy, but you don't have to choose those options. And those options aren't likely to pop up in a friendly chat.
I think it would be fun to goof around with Imoen like you used to in Candlekeep, or to tease Jaheira or Anomen for being so serious, or cheer up Aerie when she's feeling down... the possibilities are endless. And you could even have an option where you ask party members for advice like you can with your familiar, and they'd give different advice depending on where you are in the game.
This is starting to sound like such a big mod, it would have to be separate. You would probably have to have a different set of friend "flirts" for male and female PCs. After all, gender has a large impact on your friendships with either sex, and some banter flirts might work for one gender or the other, while others might work for both... I dunno... but I'm really excited about this idea.
I officially voice my enthusiastic support. I could even help out, if anyone is interested. I'm a mediocre coder, but I'd be happy to write some banters.