You should use the appropriate pronouns for a person.
Mary Ann was a waitress, and she was waiting on a man sitting at the counter.
Mary Ann wants to take the man's order.
"Mary Ann asks the man, ""Sir, what would you like to order?""."
"Mary Ann asks the man, ""Ma'am, what would you like to order?""."
The man gave Mary Ann his order, and she sent it to the kitchen.
The man is furious, and he storms out of the diner.