Stephen Harper again--this time, for how he handled the same-sex marriage issue way back when he first became Prime Minister.
In the previous Parliament, the Liberals introduced a bill to legalize it, but because of how it was introduced, every Cabinet Minister was forced to vote in favour of it (and a few quit Cabinet over it), and I personally don't like seeing MPs whipped when it comes to matters of conscience. Harper did attack the bill because the Bloc voted overwhelmingly in favour of it (saying that it was illegitimate because a majority of federalist MPs voted against it), and he promised that, if elected, he would bring a motion asking the House if they wanted to reopen the debate, and that none of his MPs would be whipped. (The NDP did whip its MPs for all such votes and kicked out one MP over it.)
And he did exactly that. The motion did not carry (though he voted in favour) and the issue hasn't been raised (at least not seriously--I don't follow these things that closely) in the House since.
His handling of the abortion issue, on the other hand--another debate he promised to leave closed--has involved effectively silencing his MPs who want to speak about it, and again, I dislike that sort of muzzling. (See Mark Warawa.) But the one time something close to it (a motion to form a special committee to study when life begins) came before the House, he voted against it.