What does this comparison mean?

2

I am not more ugly than your sister.

Does this mean I am as ugly as your sister?

4It means you are either less ugly or as ugly, but not uglier. Whether you are less ugly or as ugly cannot be deduced from the sentence. In general, I'd use uglier, not "more ugly", but that is partly a matter of taste, I guess. – oerkelens – 2014-06-19T14:01:50.710