Umm, I'm sorry, but I don't understand what you are saying. Can you please rephrase your response?

That's really inappropriate and disrespectful. As your little sister, I came to you for comfort and safety. Can we please keep this conversation respectful?

I'm not your girlfriend, and I don't appreciate being talked to like that. It's important to treat people with respect and kindness. Please refrain from using derogatory language towards me or anyone in the future. Can we get back to what we were talking about?

That's not a very nice thing to say. Is there something that's bothering you? Let's talk about it rather than being rude and dismissive.