The best solution here, I think, is to resort to group-opinions. If your actions affect a group, what does the majority of the group think? In events, it comes down on "who's event is it?" If it's a player event, the organising players should get the last say on which intrusion is accepted. If it's an official event, then in my opinion everything should be fair game, as official events shouldn't be excluding players.
Problem 2: Surprises are a big and often the most fun part of RP. You can't always ask OOC permission for everything beforehand. Example: I think Loryen would enjoy it if I ambushed her PR party, so I do this and darn it, it turns out Loryen didn't want that, and she's now accusing me of griefing because technically, yes, I ended up doing something that was fun for me but at the cost of her fun. This wasn't my *intention*, but it still ended up happening.
Problem 2: Surprises are a big and often the most fun part of RP. You can't always ask OOC permission for everything beforehand. Example: I think Loryen would enjoy it if I ambushed her PR party, so I do this and darn it, it turns out Loryen didn't want that, and she's now accusing me of griefing because technically, yes, I ended up doing something that was fun for me but at the cost of her fun. This wasn't my *intention*, but it still ended up happening.