Genz, let me get this straight, you are his client and he spoke to you like that? I think, in all honesty, my response would depend on my seniority and the importance of his firm to my employer.
I wouldn't give him loads of facts. Why should you waste your time educating him? It's not your job nor your responsibility. I'd say something like:
Thank you for the response, but you must have misread my email. I said one beer, not levels where FAS is relevant. I thought lawyers were meant to have an eye for detail. Hope you'll do better than that at our seminar
Or something along those lines. Tells him to fuck right off without massively engaging or spelling it out. If he followed up and argued his point, I would report him to his supervising partner (assuming he isn't one).
If you are very very senior - thinking of a client I knew and how she would respond, she would say
I didn't say I was drinking heavily and you are clearly very misinformed about FAS. I find it offensive that you choose to lecture me in this way as I am very well informed on this subject and I am your client not a child. I hope you will see fit to apologise.