Mine was today.
I had literally every Pokemon up until SuMo. 800+ of them.
My save data corrupted and if I don't want to keep a useless cartridge forever, I have to delete them all. I had events from as long ago as 2009 on there and there's no way I can recover those without buying a WEP router for DNS hacks Damn you, Gamefreak, and your lazy programming.
The very first game I remember that made me cry was Telltale's "The Walking Dead". I got misty-eyed throughout various moments, but the ending is an absolute tearjerker.
When I was like three or four, Sonic 2 for gamegear was my first video game. So the premise of the gamegear version is Tails was kidnapped and you have to get him back. But after you beat the game you don’t actually get him back, you just see his face formed by stars in the night sky. So dumb toddler me thought that meant Tails was dead. I laughed so hard I cried.
Beyond Good and Evil. First, when the lighthouse is destroyed and all the kids are gone. And then, when you finally find Pey'j after he's captured, but he's dead. Yes, he comes back to life but still...
Tetris. When I lost one time. I even threw some things. Those damn blocks didn't know how good they had it with me. Why couldn't they just go where I wanted?