Bella (a sweetheart 99.9% of the time) is developing a really awful habit. When people come over she barks like crazy, non-stop until they sit down, and sometimes longer. After awhile she calms down and wants to be their friend, but just until they stand up again and then she tries biting their pant legs (this will be a huge problem when its not cold and people are wearing shorts!) We can't let anyone pet her if she doesn't know them really well because we can't trust her to be nice, she tried to bite someone yesterday. What should I do? She has never been friendly to UPS people but lately she's mean to all guests except for my cousin (over all the time) and one of my friends, and my grandparents. Shes especially aggressive towards my brothers friends. I don't know what to do. I know this is my fault, maybe she wasn't socialized properly or something. She's such a sweetie around people she knows. What's weird is she makes up her mind about people automatically. Bella has always been especially loving towards my cousin, but especially mean to my brothers friends, whats the deal?