Don't be that guy.
Your best friend, a bartender, is talking to someone else, so the new girl comes to help you and actually charges you full price for your drink(the hussy!). Your first response shouldn't be to namedrop.
Your best friend normally gives you a discount at the boutique she runs but she is out of town. How dare her sister not give you the same discount!! Ridiculous!
You know who else knows the owner?? The people that work there. You aren't impressing anyone. Your friends actually expect more patience and understanding from you because you know them.
You know what will actually get you more discounts? Not supporting your friends just when you are getting free shit.
Oh, and always over tip.