The same as spoiling but with a twist. It is saying that a character did not die in the movie and is still alive instead of telling the person who dies.
Mark: Oh boy I’m about to see endgame!
Chris: Nice! You know Thor doesn’t die!
Mark: Damn it chris! You just second hand spoil!
Chris: Nice! You know Thor doesn’t die!
Mark: Damn it chris! You just second hand spoil!
by Citorealia May 4, 2019