Is there anything you didn't realise was bad manners until you were an adult. Things you weren't told when you were young? I didn't realise it was good manners to leave your alcohol at a party when you were leaving until I was in my late 20s. Always took my half full bottle home with me! Cringe. My friend was never taught it was bad manners to start eating before everyone's meals had arrived until she was in her 30s. She was always half finished before everyone had been served.