If not stated specifically otherwise, low-res with text on the bottom or side with your copyright info, not to be reproduced without permission - so and so. Perfect for e-mailing. Toss in a few cheap 8x10 prints and hope that tides him over from ever trying to get more prints made. If he does complain explain that like you told him on the phone, you do not allow others to reproduce your work and you were the bigger person to give them some prints. Tell him that no cheap drugstore lab could ever reproduce the images at the quality you intended but since he's a friend you would give him additional prints at half price though - which should still be over your cost to get them printed. Sounds like a cheapskate so if you make him think he's getting stuff for free or dirt cheap, that may appeal to his thick-headed side.
Kill 'em with kindness!
If he checks with any self-respecting Photog he'll learn that a CD of full res digital negatives is like GOLD and would never be given away for less than several hundred dollars.
But on the other side, I understand the desire to shut him up and wipe your hands clean.

, especially not if you do it for friends) and give a medium resolution CD with the option to order from you for just your own costs, as you can only guarantee this way that the quality of the images will turn out good.

