1) What's the occasion? どうしたんですか? "What's the occasion" is a fairly common question when somebody is offering you something nice and when you're wondering why. "Occasion" is often used with the word "special," "a special occasion," something that needs the special recognition but it can also mean a reason or an opportunity and it's also use sometimes for vaguely kind of social event. So when people ask, "What's the occasion," they usually mean something like, "Is it somebody's birthday?" "What are we
promotion?" something good like that.
2) QT = quiet "QT" is kind of an interesting thing to say. It's slang for quiet, keep it quiet, keep it secret. And it probably comes from people using the first letter and the last letter of the word quiet. Occasionally I think you see it on the "Q and T," although I usually hear it without the "and."
Keep it on the QT. = 秘密にしておく、内緒にしておく。(口語)
3) take it for granted "Take it for granted" is a phrase that means we understand it, we don't really need to talk about it. It's a given.
新しいことにチャレンジする期待感と不安感がミックスされているということ That's right. You feel both happy and worried at the same time.
5) liaise "Liaise" is sort of a newish verb that was created from the original noun "liaison." When you take a noun and make a verb out of it, that's
starting out with the verb and changing it into a noun. A couple of other examples are "escalate" from "escalator," which was originally a product name, and "burgle" from "burglar."
6) millionaire 大金持ち In English, when you talk about a rich person, you often call them a millionaire, meaning they have a million dollars. Nowadays a million dollars doesn't go as far as it used to. It's not so unusual to be a millionaire, I guess, although I'm not one. But we still use the phrase generally to mean somebody with a lot of money.
7) color me + 形容詞 or 名詞 私を~と呼んでください。私は~です。 The phrase "color me" usually followed by an adjective, although sometimes an actual color is used... became fairly popular in the 80s, I think. And it just a way to describe yourself. Some other examples that you might hear are "color me skeptical," "color me shocked," "color me unimpressed" or "color me stupid." They are all kinds of ways to describe yourself.