Happens to me few weeks ago...
Me: AircraftABC climb to and maintain FL330, further climb in 4 minutes due to opposite traffic above.
Pil: Climb to FL330, AircraftABC.
...
(STCA advisory on my radar due to high rate of climb)
Me: AircraftABC maintain FL330 when reaching opposit traffic above.
Pil: Maintain FL330 when reaching, AircraftABC.
...
(C Mode on my radar display FL320)
Pil: Approaching FL330 for higher, AircraftABC.
Me: I SAY AGAIN, MAINTAIN! Traffic above, 12 o'clock, 6 miles opposite direction.
Pil: ...Traffic in sight and on TCAS... AircraftABC!
Other Pil on frequency: You're damn stupid!
Another different voice: Oh, yes you are!
