i like to test my customers' sense of humor whenever they mention having sympathy for our hours ( usually this happens after closing time, and it is obvious that we are all there because the customer took so goddamn long to say "yes"

)
"You have such rotten hours. sorry we're keeping you here late."
"Oh, no big deal. I only worked half a day today.[dramatic pause] 9 to 9."
"Oh, OK"
this tells me if they're paying attention or not. also can indicate intelligence. If i have to explain that it's a joke and why it's funny..."you see, uh...12 hours"