MJ
Tough call. Never come across one like that. If the checkout was substandard then retraining is easy to recommend and most people will accept it, but it's not easy to stop someone from flying if they have acute air rage.
Was he just having a bad day?
Then again in your part of the world, where else could he rent an aircraft if you deemed him to be "in need of additional training" for whatever reason. You don't have dozens of airfield with flying schools up there. If he really was a fruit cake then you can aford to lose that kind of business before he does some damage either to himself of somebody or something else.
Having said that I don't know what I would have done there and then if that situation arose. It's all very easy to ponder in front of a keyboard.
Only problem you then face if he is unhinged and you just obliterated his ego is remembering to shower without a curtain!!!
jsf
