If a girl in your own age group calls you mister, is that flirtation?

silentlambintj1
I'm 20 and work part time as a bartender (full time right now due to the fact I'm not on break.

Anyway, as a bartender, I make drinks for the lounge side and restaurant side. There's this waitress.

We were both having rough days. I said "can you kill me" and she said "I'm going to kill myself."
I the said "I'm worse than you today."

She then said "listen mister, you'll be out of here in an hour. I'm here until closing. She then started laughing while another waitress was beside her laughing.

Am I overthinking things? Or does she have a crush on me?
If a girl in your own age group calls you mister, is that flirtation?
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