Today at work I addressed a male as Mrs. since the first name was Frances. My face turned red as he walked up to doorway. 
I went to call a patient back to be seen and I addressed them as Mrs and the person that walked up was a male. 
user
Oh no. How'd they react?
assistant
He didnt get upset.. He said it happens alot, but I can feel my face get red!
user
I'd be super embarassed, too!
assistant
Yes it was very embarrassing! we both laughed at it. 
user