I am not going to explain the basic, like "who's Sailor Moon?" and stupid sh'uff like that, ok?
Here are the obscure stuff...
Pocari Sweat: Yes, this is an actual beverage. I have seen it, I have smelled it, but I'm not gusty enough to drink something named after something that comes out of my glands. Silly Japanese advertising. Anyway, it's basically a drink based on beans, or something, ok? Oh, and the commercial is, of course, a parody of the norm of Japanese TV ads.
Lain: If you don't know who Lain is, you need to be tied to a chair and made to watch her show (serial experiments lain) while someone makes an experiment out of you! <---heartless, and powerless, threat. Anyway, she appears because of Ruri Hoshino: both are little girls in love with their computers.
In Layer 6: Kids, she talks to a persona in the Wired that is represented by a big snickering mouth. Tired of the mouth's constant yapping, she say to it, "Be quiet Cheshire Cat." This leads us to...
The Bunny Suit: In one of the earlier episodes of Martian Successor Nadesico (not sure which one it is right now, but I'll get back to you on that), Yurika, Ines (the doctor), and Ruri made a little show explaining all sorts of things concerning the Nadesico. Yurika wore a huge white bunny costume that looked like something from a theme park. And don't ask me why I had it on. I just did.
Misu/Miss: Just a play on how it's said in the Japanese version...wait, that's explained...
Cupid at the Book Depository: Only an idiot cannot get this one. Lee Harvey Oswald was said to have shot President Kennedy from the highest floor of a book depository.
Lemon Warning: You're not getting help from me there!