I remember one actor on a talk show saying "Good question. And I’m sure [my well-known character] would have a clever reply. But that’s because he has writers coming up with that stuff for him.
People meet me and they expect witty repartée, but that’s not me!"
IIRC, Michael J Fox once said he got lots of excited questions about time-travel, and he’d apologetically reply, look, I’m just an actor; they pay me to stand next to things and say stuff…
Not too long ago, my brother and I were fixing something in the basement when mom came down and asked what we were doing. In unrehearsed unison, we said, “making trouble.” It was almost creepy.
But when it happens it’s pure magic! It helps if you have a store of snappy lines saved up for when the opportunity presents itself.
For example:
A: I have to write an obituary for this guy. 
B: How about “He was a fine gentleman, a great scholar, and a wonderful human being”?
A: Have you ever seen Snatch? (The movie.)
B: Many times, many times… (Not the movie.)
A: Would you like to pet my pussy?
B: Move the cat and I will!
All of which I’ve used at one time or another. 
But, have you had a chance to use “I am afraid I will be unable to attend the funeral, but I would like to say that I approve of it.”
That’s a good one!
If invited to a wedding, I say “Sorry, I don’t do either weddings or funerals.”
Did you know, BTW, that Lucille Ball normally refused to attend funerals? If she did, it was a sign of high respect for the deceased.
Kind of off topic for the thread but here goes (former demo range instructor hat on). Shock tube is a plastic hollow tube with high explosive material deposited on the interior wall. HMX HMX - Wikipedia is commonly used. It can replace detonating cord (plastic tube with solid explosive core usually PETN Pentaerythritol tetranitrate - Wikipedia) in many applications. Det cord and shock tube both transfer an explosive shock wave from a firing device to an explosive charge over a distance. The shock tube is considerably smaller in diameter (3mm and 2mm minitube) by about half and hollow. It’s much lighter and more flexible than the det cord.
One area were shock tube does not replace det cord is in demolition ground work where substantial earth cover is required over the explosives to be destroyed. A shock tube assembly (see below) has a detonator at its terminus. Detonators are sensitive somewhat to shock and are never buried for safety reasons. (Earth cover thrown on may contain rocks, in case of a misfire you don’t want to go digging for detonators). Typically the explosive donor charge (molded C4 plastic explosive or TNT blocks) has the det cord embedded in or wound/knotted around the charge with a sufficient length (loop) to extend out from the pit/earth cover to allow attachment of a detonator visibly above ground. In case of a misfire, a new detonator(s) is/are attached to the det cord and initiation is tried again.
A shock tube assembly (initiator at one end and detonator at the other) is used to replace electric blasting circuits in areas with electric fields or electromagnetic transmissions could induce currents in the firing wire prematurely detonating the system. Film blurb from Ensign-Bickford Shock Tube Assembly (STA) - Ensign-Bickford Aerospace & Defense is a good rundown.
Thank you for your attention, take a smoke/snack break.
Very subliminal. 
I know, right? MAS*H alone provided a lifetime of snappy comebacks:
A: Now, will you walk this way?
B: If I could walk that way, I wouldn’t need the talcum powder.
My favorite line from MASH is the one spoken at the memorial for the man who never was:
“You might say we made up Tuttle.”
That is a funny line, but I was referencing mine as a snappy comeback.
Another example, for when anytime someone gives a convoluted and unlikely explanation for something:
"Meanwhile, Aunt Martha, having taken a tromp through the woods, is lying in a ditch at the edge of town."
Or:
A: “Who’s Walter?”
B: “It’s my given name.”
A: “Give it back.”
A Groucho line, originally, I believe.
The destination shown on a bus is always exactly where the protagonist needs to go.
Well, of course. Why else would he/she get on it? DUH! 
The bus does stop at other locations too. Not everyone goes to the end of the line. But it does seem like it’s always the end of the line for the protagonist.
I thought someone already mentioned this, but I can’t seem to find it… Whenever characters have to fly somewhere, there’s always a nonstop flight available, no matter how big or small a city they’re traveling to or from. Usually, I just tell myself that they connected somewhere but they just didn’t show us that part. But I just started watching the latest season of Ted Lasso last night. When Ted sent his son back home (from London Heathrow) you actually hear a PA announcement “Flight 1234 to Kansas City is now boarding”. Which made me say “Come on, Kansas City doesn’t have nonstop flights to Europe!”
Although not something “extremely common in TV shows”, another thing that bothered me was when Ted looked at his phone to check the status of his son’s flight, it shows the the correct IATA code for Heathrow, LHR, but for Kansas City it shows KCI, which is wrong. Kansas City’s IATA code is MCI. Airport codes in the US aren’t supposed to start with K, because radio stations use K for their call letters.
I did laugh at the improbability of a direct London-to-Kansas City flight.
But some of this is like how people can always find a parking spot directly in front of the place they’re visiting, even if that’s in midtown Manhattan. The show isn’t going to waste time showing people hunting for parking or walking blocks to the place they need to be.
They poked some fun at this in the “Simpsons” episode where Manjula travels from India to marry Apu: “Which Bombay-to-Springfield flight is she on: the 10:00, the 10:15, or the 10:30?”
Rats squeak more than horses neigh.