You are allowed to watch it with your friends though, of course that might depend on the country you live in. In Germany you are even allowed to give copies to close friends and family members (but you are not allowed to break copy protection).
You have a point that you can provide a "public performance", but as I understand it (clearly IANAL) that is defined quite strictly and you may show friends and colleagues in a private setting at will.
You are not allowed to show to an audience a movie you bought on a dvd. There may be other examples.