There's nothing more annoying than hearing random people telling you the same thing on a daily basis. Especially if it's a lame joke that you're supposed to laugh so the customer can be a bit comfortable of what they're doing.
A customer comes into my checkout line and unloads his groceries only to find out that my line is a 10 items or less express line.
Customer: Oops, looks like I have 11 items! Hahahahahha...
Me: LOL ... I haven't heard that one before!
Customer: Hahahaha ... I'm such a comedian!
Me:: Hahahaha... you're killing me!
Me: Alright ... paper or plastic?