It 'can' be done nicely. This morning a driver waves her hand at me thinking I'm doing something wrong. I'm pretty sure I know what she thinks I've done and seeing she is joining a queue I turn round. No intention of getting angry, and she has kids in the back, I'm not going to put myself in the position of being 'aggressive'.
Putting on best spoken lawyer voice, "I'm intrigued as to what you think I did wrong"
"That's a no right turn" (yip, I was right)
"Ah, if you look underneath there's an 'Except for Cycles'"
"Oh I'm sorry, that's my mistake, I apologise"
"No worries, have a nice day"
"Thank you, you too"
Exeunt.