It's apparently very rude to say that you aren't interested in something someone wants to talk to you about.
I didn't know this for years. My husband eventually told me that it is considered ignorant to say that you don't care, even if you don't care.
Apparently it is nicer to pretend to give a shit about something than to save someone wasting their breath on something you don't give a monkey's about [boggle], so you have to sit there, nodding nicely, while they go on and on and on and on about something so dull you wonder if you could fake a heart attack to get out of there.
What I think is rude is someone expecting you to be their audience and not giving a shit whether or not the subject they have decided you must listen to is one that interests you.
That said, even I think that telling someone to "shut up" is rude. You should have said look, I love you, but I am really not interested in this subject, why don't we talk about something we both like.
Or excused yourself, saying you needed a huge shit and might be a while.
DISCLAIMER - if you have slept with her sister/mother/brother, emptied her bank account, kicked the dog, got her gran pregnant or otherwise been a shit and she wants to talk about that and you want her to shut yup - you're an arse.
If it's who did what in eastenders, then it's ok to not care and to say so