Pirate Tower. You'll have to sneak your way in, but it's rewarding.
Go on the Great Park Balloon with about 25 strangers, all of whom are ignoring each other and taking pictures for their Instagrams. You can do some pretty good photobombing and piss them off.
The Shake Shack is a nice little place to watch pretty girls (or guys) and have a shake.
Favorite thing to do? Photobomb people taking selfies with celebrities. Just stand there and look confused at them.