Why are you so quiet?

I say "no one plans a murder out loud" with a devilish smile

I'm quiet because I am judging you silently in my head. I have determined that you are a dumb fuck. That's what I would say.

Here are some other responses:
Flip a table over, scream "YOU'RE QUIET!" and run off on all fours
"AM I SUPPOSED TO BE LOUD?!"
"...Not when I fuck your dad"
"Your haircut is unsuiting to your face shape"
"何か。英語が分かりませんよ。あなたの口は汚そうです。"
Scream "WAKA WAKA" then tweak their nipples and run away

One of these things is not like the others.

The last one is actually plausible because we know how to put a bee in our mouth. I'm assuming it'll work for wasps too.

I say "wait, you can see me?" and then just walk off.

Gotta try these...