Bipolar or just mean
Friends and family throw "pscyhobabble" and diagnoses around very freely when they just need to work out their difference or face character flaws and grow up.
Bipolar does not equal "mean." most likely, you sister is just trying to hurt your feelings by "labelling" you. You would both do best to get facts from the nami [google this] website about what "bipolar mood
disorder" really is.