some yrs back, S. of Karachi, we were a bit in front of SQ for a crossing point, F370, SQ instructed to descend to 330... long argument, in the course of which SQ asked us would we mind them crossing astern of us visual!!! (Daylight, VMC.) We weren't interested in that and the argument with Karachi ATC continued - eventually we picked him up visually steaming steadily in from nine o'clock - at the last moment he obeyed Karachi's increasingly urgent instructions, last seen in a gentle descent 500 or 1000 metres astern of us.
There is nothing you can say to people like that, and nothing constructive you can do about it.