I recall reading an estimate by an MIT physicist that if all the nuclear weapons in the world were set off at the same place and time, the resulting explosion would be short by a factor of one trillion in order to move the earth one foot.
It came from the same camp that later derived nuclear winter as the reason we should all disarm and 'live in harmony'. Not saying I agreed with them. The most intelligent account did factor in the rotation of the Earth during the all-out exchange, which, iirc, placed most of the megatonnage on the same side of the planet, in the northern hemisphere.
I'd be pretty skeptical of a large volcano causing enough of a rotational instability as well.
But a few mile in diameter Ni/Fe mass might have a different and less subtle effect. That is why I tend to lean toward an event of cosmic proportions.
What if everyone in N. America jumped at the same time. That'd probably do it too.