If you have all got together, and this is the way you feel, then you should feel duty bound to suggest that he gives up flying.
Bear in mind, that if you don't, and he then has a 'nasty', you will have to live with the feeling that you should have put a stop to his activities sooner.
By the way, have you expressed your concerns to the owner of the aircraft which he flies? How does he/she feel?
Atempting to teach someone a lesson as you describe is not likely to lead to a satisfactory outcome.
We could all make a list of people who are flying who shouldn't be.... don't let's add to the list.
[This message has been edited by Fokjok (edited 21 May 2000).]