How many personality disorders can someone have?

All of them: Personality disorders are not mutually exclusive according to dsm-iv, the current diagnostic manual for psychiatry. So in theory it would be possible to have the whole list of about ten. Usually, though, patients with features of several disorders are diagnosed as "mixed personality disorder". Personally, i'm skeptical about the value of these labels, as personalities don't fall into neat bins.

How many do you want: There is a great deal of overlap between the personality disorders. While theoretically you could be criteria for all of them, it is highly unlikely. I like to think of personality styles instead of disorders. What aspects of your personality are problematic? How does it interfere with your life and relationships? These are the issues that a good therapist could help you focus on.