Thanks for your input.
If I may, I'll just clarify a couple of points. I have been a touch ambiguous about some of the details so that the individuals can remain completely anonymous!
Firstly, the individual concerned was not really known to the FTO as he/she had only approached them for some limited recurrency training prior to the flight test.
Secondly, the abuse took place on the ground in the cockpit at shutdown, not in the air and the hostility shown prior to the flight was in the form of grumpiness and unfriendliness as opposed to overt aggression. When it comes to dangerous traits, I should point out yes, my colleague is tolerant and had deemed all of the first incidents worthy of a forceful de-briefing but not a statutory failure. It was the last incident which he deemed as being a show stopper, at which point he took control.
Regardless and needless to say, he was upset and shocked at what took place and is still contemplating what, if any action he should take next
UDUD