Yes, I am in charge

Beside the absurd FAQ's we get, and screaming complaining customers, I think my least favorite part of my job is the way customers assume I am young and dumb.  I don't know why those two tend to go hand-in-hand.  When I was younger, I was not dumb. 

I'm almost 30, but I look rather young.  In fact, I asked a few customers how old they thought I was, and their answers ranged from 16- 22!  I cannot believe someone thought I was 16 years old, wearing a wedding ring.  But for some reason, because I look so young, people assume I don't know how to do my job.  Although I happen to be the manager, with a name tag that indicates this, people still condescend to me as if I were illiterate.  A few examples:

• After a customer orders and before I have a chance to repeat their order to them, they say,"Did you hear what I said?"
• After I have put cookie dough in their ice cream and started mixing it, they say, "You forgot the cookie dough."
• When they ask to sample peanut butter ice cream, I put the taster spoon in it and they say, "I said peanut butter!"  "Right, this is peanut butter.  The one in front of it is espresso ice cream, not peanut butter."  "Oh."  Since I make all the ice cream, I think I can tell which flavor is which.
• On Saturday, I asked a woman in line if she needed anything else.  She asked me a question, and what I heard was "Do you have toffee?"  It was a little crowded, so there was a low din in the room.  I responded, "Yes, we have Heath bar."  She snapped at me and spoke with a sarcastic tone "Coff-ee!  Like you drink!!"  "Oh, no, we don't have coffee."  We are an ice cream place!  Why would we have coffee, and why do you need to snap at me and speak to me like I'm 2?
• Lots of people try to correct the way I ring them up.  They argue with me that I charged them too much, when I simply ring them up for the price that corresponds with the item they ordered from the menu

It's very draining to work with such condescending and demanding people.  I have to be patient and realize that ultimately it doesn't matter what that customer thinks of me.  I know I have 2 college degrees and that I'm a savvy business woman. I simply wish the customers would use common manners and not make such base assumptions.