It doesn't matter to me if what David has told us is exactly true, or if he has changed some of the details "to protect the innocent," or even if he's outright lied. To me, the question is purely hypothetical, since I know better than to contribute to Wikipedia as a regular user, much less as an admin.
So David, here's what you do: Accuse your enemy of vandalism. The important thing is to establish a pattern of vandalism and a pattern of warnings. Start at the lowest level, and as your enemy continues editing in any way, increase the level of your warnings. Eventually, your enemy will want to give you a taste of your own medicine, and he'll certainly be unaware that there is a policy that says "Don't give admins a taste of their own medicine" (because it's in fact called "Don't template the regulars"). Remember: you can remove anything from your talk page, but your enemy is not allowed to remove anything from his talk page.
When it gets to that point, block them for 24 hours. If your enemy comes back after that and is still not showing you the proper respect, you'll have to take more drastic measures. But if the guy really has a Ph.D. in history, I imagine he will not escalate after the block.