Heard this one play out on the radio the other month.

"Airline #### descend at pilot's discretion and maintain FL340."
"PD to 340, Airline ####"
*a few minutes pass by*
"Airline #### descend and maintain FL340."
"Descend and maintain FL340 now, Airline ####"
"I thought you you said pilots discretion, which means WE descend when WE WANT down to 340!"
"Airline ####, affirmative, but now I need you to descend to FL340 due to converging traffic that would be hazardous to your health."
*In the most sarcastic tone possible* "Ohhhh Okayyyy I guess we'll descend to FL340 for our healthhh...."

Way to berate the controller for doing his job...