First Microsoft abandoning skeumorphism with Windows Phone 7 (and later Windows 8), then Apple going to war against skeumorphism in iOS 7. That one-two punch just broke me, and it especially hurt when Apple did it specifically because of Susan Kare's history with the company. I've always despised Jony Ive's entire design aesthetic ever since the original iPod came out, but when he neutered iOS my dislike of him became intensely personal.
I still say that if I ever win the lottery and become a billionaire, I'll hire a team to make a proprietary mobile OS just for my personal use that's built around skeumorphism and trying to imitate either iOS 6 or maybe even translate '80s and '90s Mac styles to a touch-first platform.