I.S.
Poor guy...I had something similar when I was young...I would get diarreah everytime some big social event would happen, dances, dates, even school...anything.... Doctors back then put me on stronger stuff than immodium (lomitil) and I got addicted to them...I know others who did too.
In college a test realized it was STRESS. I took some stress relief therapy and I've improved so much that I never had to take that prescription again. I had to learn to relax all my body muscles, and it helped relax my intestines. Research it on the internet or seek profesional therapy, whichever is best....but punishing him only adds stress and pills are not the answer.