I Can’t Believe It’s Not Butter! – An expression used to react to something a someone is excited about that really isn’t that exciting. Like butter substitute, for instance.
EXP – “I just got a brand new pencil!â€? Jenny squealed. “ I Can’t Believe It’s Not Butter! â€? Maddie exclaimed with fake enthusiasm.

PWOMD – Abbreviation for Personal or Portable Weapon of Mass Destruction. Used to threaten a friend who is doing or saying something completely ridiculous. Actual words are never used aloud; always use the abbreviation unless someone asks you what it means.
EXP – “You said you were going to take me on a date to the water fountain!â€? Jenny yelled. “Dude, don’t make me get out my PWOMD .â€? Vanessa said to him.

You know what…? – Said when a friend insults you and you can’t think of anything to say back. Saying this effectively ends the insult and you can move on. This sentence is never completed.
EXP – “Your Mom wears combat boots.â€? He sneered. “You know what…?â€? Vanessa said.