Screw Job Finish at Starrcade 97 - This was the perfect time to have the NWO (finally) lose and Sting was set up for success, the slow count, outside interference, and perception that Hogan won clean and was robbed was a huge disappointing ending to the most anticipated match of the year in all of Pro Wrestling
This is a great answer. Sting vs. Hogan at Starrcade 97 was as close to a flawless build-up a you can possibly get. This was the absolute peak of WCW, and was the culmination of the NWO angle. The ending was so simple, Sting beats Hogan and reclaims the WCW Title. Sometimes the obvious move is the right move, you give the people what they want. This was a classic example of Bischoff out thinking himself.
The other obvious choice would be the entire Invasion angle. The decision to pull the trigger on this angle, knowing full well the limitations of the WCW roster they were bringing in, was probably the worst booking decision ever made by the WWE. As the Invasion continued, the bad decisions were compounded and the result was a terribly executed story that in no way lived up to the expectations of fans. The ramifications of this disaster rocked the WWE for years, and you could argue that it's effects are still felt today. The WWE tanked hard in terms of ratings after the end of the Monday Night Wars, and the Invasion angle ran the company further into the ground. It's a ratings hole they have never recovered from. If handled properly, the acquistion of WCW could have benefitted the WWE greatly and helped them sustain their success.
Triple H vs. Booker T at Mania 19 also comes to mind. Based on the way this match was built, Booker T had to go over. Triple H basically said that Booker T couldn't be World Champion because he was black, then he went over. It was ridiculous then, it's ridiculous now, and it's especially bad because you know that Triple H thoguht that even if he won he could "make" Booker T in that match. Because Triple H thinks he's Ric Flair. The problem is that Triple H was not, and is not, Ric Flair, and beating Booker T was fucking dumb. I wouldn't have had a problem with it if the build wasn't so lopsided, with Triple H shitting on everything that Booker T had accomplished and utilizing very very thinly veiled racism to draw heat. Having a heel cut a promo like that is fine, but you've got to see that heel get his comeuppance and see the babyface vindicated. That did not happen.
A more recent example of a booking decision that robbed the fans of what they wanted would be the 2014 Royal Rumble. Every single fan in that arena wanted Daniel Bryan to come out at number 30 and win that match. It didn't happen and the crowd shat all over everything. This finish did end up being another blessing in disguise however, as it brought legitimacy to the idea that the WWE did not want to see Daniel Bryan on top. Eventually, he would break through and would be added to the main event at WrestleMania 30, ultimately leading to one of the most satisfying payoffs in WWE history if only because the fans dragged the WWE to that point and basically forced it to happen.