Well, for certain occasions, i do different things.
If i am greeted by a nice fellow, and i am wearing a top hat and fake moustashe, i usually reply to their "Hello" with, "Good Morning/Day/Evening sir!", and tip my hat in a fine matter. Then, i continue to do a Charlie Chaplin dance until they go away.
If i am greeted by some guy, and i'm wearing a fur coat and a ruskie hat, i usually reply to their "hello" with "Eez about TIME you get 'ere, do you have zee papers?". When they say "No?", i slap them across the face and scream "GET ZEE PAPERS FOOL!", and storm away.
There are many more fun things that i do, but those are the most common.