eBay will look at his track record. They're not going to ban a guy for calling one seller an idiot if he has an otherwise clean record. If he misuses the message system regularly, they might.
If you're using best offer on the item, it was silly to lower the price in your counter-offer by such a tiny amount, regardless of the buyer's low original offer. Either decline the offer or provide a decent counter-offer.
If you're not using best offer on the item, he's not even supposed to contact you with offers, and in the future you can simply ignore the offer or respond with a polite, canned response (I use, "Thank you for the offer, but this is our best price at this time.")