I wonder what the background of the relationship is.. how they met, how long they dated, if she treated him this way during their courtship or if he got her pregnant and married her out of guilt.
It doesn't sound too much like he's tried to speak with her about it, to ask why she feels it necessary to humiliate him - maybe she doesn't realize that the tickling hurts his pride and is blissfully unaware of his contemplation of divorce. If people would communicate better, we wouldn't have these sorts of problems..
I say, he should speak with her in-depth about it, then if no lightbulbs come on, and the D word is still in mind, knock her out, tie her up, and inflict a little revenge...