I don't mind spoilers if it's something that's well known at this point like Mufasa dying, or Aerith being killed by Sephiroth, or Zelda being Sheik. I get annoyed with spoilers if it's something recent. Like the latest episode of an anime I'm following or a recent chapter of a manga. I don't even like hearing if it was good or epic or to wait for that one awesome moment. I like being 100% oblivious to it so that if there is an epic moment, I'm not waiting all episode to see it happen. It'll be unexpected and make the scene more memorable. Of course in anime they have those episode preview things but they're rarely enough to spoil much for me.
As to your experience with your friends, I'd be annoyed too. If someone starts a new anime and they were completely oblivious to stuff about it, don't ruin that experience for them. Even if you never mentioned how Itachi died, the fact alone you mentioned he did was a bad move. Especially if your friends never followed Naruto until you exposed them to it. I got spoiled that Neji died but that was before I got into Naruto so when I eventually began watching the series, it didn't bother me cause it was too late lol.