Arguably the main problem here is that he got defensive/hostile rather than refining or articulating his argument. Instead of saying "no, I'm not stupid", he maybe could have said "no, it would taste terrible and I'd probably throw up and and it may make me feel sick for a while, but the studies show that it wouldn't cause lasting damage to my body". (At least, I think that's his claim.) But then, he probably could have been more honest/clear in his original phrasing "you can drink a whole quart and it won't hurt you".
