"But I had 28 AC!"
Back in 4e, one of my players was running an Elf Avenger, with very high movement and initiative, and the ability to boost her AC temporarily.
The party ventured into some caves to find a dangerous weapon, and found it being guarded by a group of Drow mercenaries. The Drow heard them around the corner and readied themselves, so I called for initiative. The Avenger went first, then all the Drow, then the party.
While they were some distance away, she could close that distance, and did, applying some mix of things to get her AC up to 28, which was very high for that level. The Drow then went, and, having no target other than her, beat the shit out of her. Apparently the player thought he would be untouchable, and exclaimed, "But I had 28 AC!"
This has been repeated, morphed, and changed for any time a player believes that their defenses are too high for them to be harmed, in anything, and the inevitable collapse of this. It's gotten a lot of mileage in 5e, whenever someone actually gets to 28 AC (generally due to Shield and other shit) and still manages to get hit by something.
This one's actually spread to the point where people who don't even know anyone in that game are doing it, according to some of my other friends.