"Don't take it personally"

I find this phrase growing weary. Yesterday I had the bitchqueen herself as a customer. She didn't SAY she was the bitchqueen, I just assume she was THE bitchqueen based on her demeanor.
How does one handle such a person? A person with the patience of a saint would continue to smile and try to soothe afore mentioned customer and, barring that, contact a manager to come soothe said person.
Bitchqueen wasn't satisfied and stayed in my face because manager wasn't coming quick enough and I obviously was inept because I couldn't do my job (which in her book, I'm thinking, was to kiss her ass.)
My bitch tolerance level is at an all time low these days and it's pissing me off. I was about to call manager for the third time because she wanted manager to drop what she was doing and come yesterday when I saw the smug "you've got to do what I say because you're a nobody" look. I slammed down the phone and walked away. Yes, I was wrong to slam the phone. Slamming the phone was better than verbalizing my feelings of her rude, holier than thou treatment.(at least that's what I'm telling myself)
So, while I'm hiding in the back stock room trying to regather what dignity I have left, Manager takes care of customer. She comes back and tells me "Don't take it personally". The other customers behind bitchqueen tell manager they would have blown 10 minutes earlier than I did. Thing is, I'm NOT taking it personally. There are all kinds of people who, for whatever reason, have bad days and don't stop to think about how they are acting. It's not a big deal. I've had far WORSE than that dished out at me. I'm pissed at myself for SHOWING my displeasure at being treated like a doormat.

I have always believed and followed the tenet, treat others as you would be treated. I have always treated others, no matter what, with utmost respect. I hold myself up to high standards and find I can't reach them lately. Slamming the phone falls short of my expectations of myself.

Maybe I'm just taking myself too personally.