Derived from the movie "Bad Santa" this phrase has been ranked in the top most annoying questions. The beauty of it is simple. Most people after being asked repeatedly will get very annoyed, asking what "lettuce" means. In which case you can just say, "just lettuce..?"
Bob- How much lettuce do you want?

Random guy- I dont want none lettttuce!

Bob- o-kay!
Get the How much lettuce do you want? mug.