If your friend describes you as la-di-da, she thinks you're a pretentious snob. Maybe it's that fake English accent you're always using.
La-di-da is the perfect informal term for someone who acts grand and pompous. Sometimes people who speak using flowery language or long, complicated words are described this way, and sometimes it's their affected manners than earn them the la-di-da label. The word dates from the late nineteenth century, and its nonsense syllables mock the way affected people speak.