I wish I could do that at work period.
Period.
Singing doesn't even have to be a factor.
(I'm a cashier)
"Would you like a drink?"
"sure."
"What size drink?"
"What do you mean?"
"*Points at the small medium and Large cups*"
"I don't understand."
"... *WHACK!!*"
*

*
"*WHAM WHAM WHAM!*"
Up until the whack part, this was a real conversation with a student holding a very thick bio chemisty book.

You're gonna fail that class kid. In fact, you're gonna fail collage, apply for my job, and fail that too. Because you cannot understand small medium or large sized cups. -_-
(btw, I just threw, yes, threw the small cup at him rather than explain the differences in the cups is the total mass of liquid that can be held in each cup. ^_^)