What would you do to people who gives spoilers?

i would like a spoiler

I would refuse to associate with said person...

for two months!

You should let him taste his own medicine!! Try to find out what series or movies he's about to watch and give some huge spoilers about them. Then he would maybe understand how mean it is to do that.

Game of Thrones sucks(all die)

I would not care. Big deal, you'd find out sooner or later anyway.

So personally I think you're thinking too much into it. However, if your friend was spoiling something on purpose with the intend to make you angry, maybe you should find friends who don't try to make you angry. Also in that case it would seem you gave him what he wanted- you're obviously pissed.