It annoys me every single time when people react to a 'do you mind' question with 'of course' or 'sure' when they actually mean they don't mind. It's linguistically incorrect, makes no sense and causes confusion for people who actually care about using language correctly.
When they do mind, what do they answer? They can't just say 'yes' because other stupid people that have learned that people say exactly the opposite of what they mean will think it's all right. So they'll need to make a full sentence to make clear what they think about it. It would be a lot easier if we could just say either 'yes' or 'no'.
Why does almost everybody keep making this mistake?
Why are you wearing that stupid man suit?