Yeah, The Rock becoming the Corporate Champion at Survivor Series 1998 took me by surprise. Also, Shane McMahon screwing Austin over the same night. Shane had only just appeared as a regular character on WWF TV a few weeks preceding that and was the guy responsible for signing Austin to a new contract after Vince fired him at Judgment Day 1998. Didn't expect to see him screw Austin over during the bout with Mankind.
In a similar vein, Stephanie McMahon siding with Triple H at Armageddon 1999. Brilliant move and one that even ended up changing the future of the business (both on-screen but especially off) when you get down to it. Thanks Kevin Kelly (it was actually his idea.)
Austin "selling his soul to the devil" (i.e. Vince) at Wrestlemania X-7. Didn't see that coming and for good reason - it didn't make a goddamn lick of sense. Didn't see Austin turning on his team and joining Alliance later in the year either. But I wasn't as much of a smark then. Nowadays, I would call Austin joining the Alliance almost immediately.
The only thing shocking about Bryan turning on the Wyatts was that it happened after only two weeks. Who didn't know that would happen eventually?