So many!
I am an academic and use the title 'Dr' sometimes and 'Ms' sometimes. Not really arsed. At the time I registered with my GP, I wasn't yet married to now-DH.
GP receptionist pursed up her lips and altered my title from 'Ms' to 'Miss'. In front of me!
Buying furniture. I handed the salesman my debit card. He tried to refuse it. I am actually serious. He looked a bit shocked and sort of waved it away. I insisted (obviously, as I wanted to buy the furniture) and he took it eventually, saying to DH 'I hope you're taking her somewhere nice for lunch after this.' - !!!
Taking out National Trust membership, again before married to now-DH. NT volunteer insisted on putting him first as the 'principal member' despite the fact I was paying and it was my idea to join. When I rang up later about the membership they would only talk to 'my husband' - !
Being admitted to transitional care ward after having DTs - this was last year - MW unable to believe that DH and I are married despite having.......wait for it....... different surnames . She kept shaking her head and saying 'Quirky. Veeery quirky.' She was about 30, too!
When getting married, registry office clerk asked me if I would be changing my name. I said no. Fine. 15 minutes later they come out with our certificates with correct names on, but in an envelope marked 'Congratulations to Mr and Mrs DHName'. These are people that do this for a living!
NDN returning post to us that had been accidentally delivered to his house. 'But I nearly didn't, because I thought it must be a mistake, as it says Dr on the envelope and your husband's not a doctor, is he?'
So bloody tedious.