If I felt like I was mumbling when I first said it - sure, I'll repeat what I just said, once. Twice I'll start to get annoyed.
If I'm sure I was talking clearly - then I'll repeat, but I'll start getting annoyed already.
So basically, I'll repeat what I said, to a point (I think three repeats is my limit), but I'll probably get louder and angrier with each repeat. I hate repeating myself, usually. :P And if the person still doesn't get it...well. I think then that's time for angry sigh and then trying to find another way to get my point across. Or else I'll just give up.