Heard in the USA many years ago:
Fighter Jock: XXX Approach, FJ at Point Alpha for recovery.
Approach: Roger, FJ, you are number 17 in line behind 16 heavies.
FJ: Errr, in that case I am declaring a fuel emergency.
Approach: Roger, you are now number 1.
FJ: Ahh, good, in that case I'm cancelling my fuel emergency.
Approach: Roger, you are now number 17 in line behind 16 heavies.
After a very long silence -
FJ (very quietly): XXX Approach, FJ declaring a fuel emergency.
I didn't wait for any more.