When you accidentally spoil something for someone and then attempt to make it up by yelling out "Spoiler alert!"
It will nonetheless piss
someone off because either a) you're just rubbing it in that you spoiled
to an amazing
movie/book/show, or b) they weren't really
paying attention before and would have missed the spoiler, but because you had called
attention to it, now they are aware they have been spoiled
Kris: "So I'm reading this
book and so far I don't like that
Melissa: "Yeah I really
hated Snape in the 6th book when he killed Dumbledore but everything worked out in the end."
Kris: "Ye- Wait. Snape KILLS Dumbledore?!"
Melissa: "Er, ah, um, SPOILER
Paul: "Wow, Melissa, way to pull a post-facto spoiler
Kris: "It will never be the same!" *sobs*