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Quotes: Stealth Hi/Bye

"Okay, that's it. I'm putting a collar with a little bell on that guy."
Xander regarding Angel, Buffy the Vampire Slayer

"Sorry. I didn't see you, so I should have known you were there."
Buffy regarding Angel, Buffy the Vampire Slayer

"COR BLIMEY! Quit sneaking up on me like that!"
Yangus, Dragon Quest VIII

Rhea: Hey! What the- Where the hell did YOU come from?!
Death: That answer is somewhat complicated. Why not settle for a friendly "Hello"?

"Hi, Jackie!"

Harvey Dent: I knew the risks when I took this job, Lieutenant. (to Batman) How will you get him back any...
(Batman has already disappeared)
Lt. Gordon: (shrugging) He does that.

"Seriously, why do this year's freshmen keep on appearing and disappearing all the time? It feels like they're messing with us."
Riko, Kuroko No Basket

(Catwoman disappears)
Batman: So that's what that feels like.
The Dark Knight Rises (the exact same line is also used in Kingdom Come, when Superman pulls it on him or when the Flash pulls it on him in Justice League: The Flashpoint Paradox)

(Ziva appears out of nowhere)
Mcgee: You enjoy doing that?
Ziva: A little, yes.
NCIS

Ms. Marvel: Where'd Nick Fury and his little gang of terrorists go?
Spider-Man: Where does he always go? He went poof. It's his super-spy trademark.

"Boss, you're very stealthy."
Tony (after Gibbs just appeared out of nowhere once again), NCIS

"Gah! Penny, where'd you come from!?"
Ruby, RWBY

Jim Gordon: Partners are equals, Batman! When have you ever treated me like your equal? Partners, for example, tell you their plans! They keep you informed! And they sure as hell don't walk out on you in the middle of a sentence!
Batman:...I've never been good at saying goodbye.

"Now I know how Jim Gordon feels."
Batman, after Huntress does this to him in Justice League International issue 26.

Agent Washington: "Meet me at the ship."
Church: "Okay, what's the (turns to look at Washington)
*Beat*
...signal. God dammit, I hate when they do that."
Caboose: "Do wha - Hey! Where's Agent Washington?"