Him calling you an idiot isn't an ad hominem. It's only an ad hominem if he's arguing "You're an idiot, and therefore you are wrong ". "You're being an idiot, a

Him calling you an idiot isn't an ad hominem. It's only an ad hominem if he's arguing "You're an idiot, and therefore you are wrong ". "You're being an idiot, and here's why: <reasons>" is just impoliteness.