The ascendancy of the British Columbia Social Credit Party and Premier Wacky Bennett and their forty odd years of crazed highway building and bond burning. All of it. Special mention must go to the 1952 general election that gave them their foot in the door, though. Here's a rundown.
A coalition of the B.C. Liberal and Conservative parties had governed the Pacific province in coalition since 1945. The pact was formed as a result of the insurgence of the socialist B.C. Co-operative Commonwealth Federation (CCF), the predecessor to the modern New Democratic Party. However, voter fatigue was starting to get to the government and the CCF seemed ready to make a rebound.
To pre-empt this, the Coalition used their majority in Victoria to institute an Alternative Vote electoral system. The idea was to shut out the CCF by pooling Liberal and Conservative votes such that, if one party's candidate lost, the votes that went to that candidate would go to the other's by use of second preference flow. Easy path to victory there.
That came shortly before 1951, when the Conservatives withdrew from the coalition. In 1946 and 1947, the two men instrumental in bringing the pact together - Tory leader Royal "Pat" Maitland and Liberal leader and Coalition Premier John Hart - died and were succeeded by the dueling personalities of Herbert Anscomb and Byron Ingemar "Boss" Johnson. Anscomb wanted the Tories to have a larger role in the coalition, while Johnson rather madly believed that the Liberals didn't need the coalition and could run everything on their own. All this caused the coalition to fray, which led right up to the election.
There was a certain, rather arrogant, belief among the higher ups in both parties that the province could return to a Grit-Tory duopoly, this time on opposing benches once again. But they were playing to win by gaining seats, not by shutting out the CCF. The old animosities returned, and loyalists followed along to try to keep either party from making it into the second round votes. But if that meant eliminating the Grit or Tory, who to put in second. Sure as hell not the hated CCF. By and large, this left one last party, the only other one running candidates in all the ridings (sans one) - the British Columbia Social Credit League.
On the other side at the CCF, they were buoyant in the polls, supported by an "Anyone But Grits and Tories" contingent as a result of voter fatigue and the government's infighting, despite the party being led by the same person leading it since 1938. What they failed to consider was that quite a large number of CCF voters, being from that contingent, were inclined to put another party in the second preference. The only other contending party in nearly all the province? Social Credit.
It must be noted, the B.C. SoCreds at this time were merely an appendage of Alberta's SoCreds - its "interim leader" was the Reverend Ernest George Hansell, a sitting Alberta MLA whom Alberta Premier Ernest Manning appointed to run the party just for the election. In effect, they were leaderless, going into an election that even they had no expectation of winning.
And yet, when the votes were counted on June 12, 1952, Social Credit had a plurality in the Legislative Assembly, with 19 seats - just one more than the CCF - and 30% of the popular vote. Boss Johnson and Anscomb lost their seats, their respective parties reduced to just six and four seats respectively.
So now SoCred was tasked with forming a government, but first needed a proper leader. A caucus vote chose one of the three in the party with any prior political experience in the Legislature - William Andrew Cecil Bennett, the independent MLA from South Okanagan, who had defected from the Tories after losing in a leadership election against Anscomb in 1951 out of his frustration with the coalition, and in December bought a SoCred membership.
While all this was happening, SoCred and the CCF were scrambling to form the government. To that end, both pursued MLA Tom Uphill, who was a radical leftist who found the CCF "too conservative". The CCF argued that although Uphill wasn't part of their party, he was still a leftist and by that virtue they had an equal number of seats with the government, hence they should form the government. Bennett, however, foresaw this and pre-empted it by securing Uphill's support for the SoCreds. Except he changed his mind again and backed the CCF.
At this point, Bennett anticipated that he could get a stronger mandate with fresh elections, and he deliberately engineered a school funding proposal into a vote of no confidence in April 1953, leading to a new snap election called for June 9, 1953. This time around, with Bennett at the helm, SoCred decided to abandon campaigning on the monetary ideology that they were founded to institute, and instead ran on socially conservative populist rhetoric. This was a huge draw for Tory voters, their defection helped in at least some part by the provincial party rebranding as the Progressive Conservatives in order to tie itself more closely with the federal party (why they didn't do it sometime in the eleven years before, I don't know). This time, Social Credit won a majority in the Legislature with 28 seats, increasing their overall vote share by 10%. And so began an almost unbroken chain of Social Credit governments until 1991, almost as unbroken as the chain of highways built by Minister of Highways Phil "Air pollution is the smell of money" Gaglardi, built "in such shape that motorists will avoid the language which would deny them access to the highway to heaven."
TL;DR: Two opposing parties decide they hate another party more, devise a new electoral system to sabotage their representation, end up hating each other again anyway, totally different party swoops into power out of absolute nowhere because the other three are too busy sabotaging each other. Hilarity ensues.
As an aside, Bennett actually scrapped AV for the 1956 election and reverting to FPTP, despite it being the system that brought Social Credit into power. Everybody predicted that it would be the end for Social Credit. Guess what? Social Credit ended up winning in a landslide, with 39 out of 52 seats.
Anyway, it seems British Columbia has learned its lesson - preferential voting appears to be unpalatable to most of the province, amplified after complications resulting from two referenda on changing the system to STV in 2005 and 2009. The incumbent NDP government, riding on its usual hobby horse of proportional representation, has instead made this round of electoral reform one of dual-member PR, mixed-member PR, or rural-urban PR. Though in the latter case, the division of urban and rural ridings will see the latter have MMP while the former will get STV, so the spectre of ranked voting hasn't fully faded. Yet.