One day in the middle of the ocean, I had to try to contact another aircraft, as a request from ATC.
So he might have been out of range of the ATC station, when we were still within.
I therefore tried first on this frequency - no answer. So I tried on Guard - and before I got any answer (which he gave by the way one minute later, on this frequency) some idiot started to bla-bla, with the grave accent they usually take in this case "You are on Guaaard "
so my answer came quickly " I'm on Guard, for good reasons, shut up please" and that was all !