Caporegime
My 4 year old still does this, I was always suprised in the sort of people that spoke back, Strangely it was either teenagers or old people, ages from about 30 to 50 just ignored him.
Does not take a lot to be polite.
My 4yo wants to talk to everyone. One of her tricks is to put her teddy bear on the conveyor belt at Tesco. Very few of the checkout girls will play along with her, but she loves it if they "beep" him on the scanner and get her to pay for him.

T-shirt worthy quote that. "We should warn the gerbils anyway". Would be a difficult t-shirt to explain though. 



"You can't say that! Who taught you that?"