Gag Echo

A subtrope of Meaningful Echo, the Gag Echo is a pretty common trope in fiction and while it's found in works outside the comedy genre, it's always Played for Laughs. The line of dialogue will often appear in the form of a Brick Joke though it can pop up pretty soon after the first line. Usually the line will be repeated by another character and part of the fun comes from them not knowing someone else has already said the same thing. It can overlap with the Ironic Echo but differs from that since the Ironic Echo isn't usually played for comedy and the Gag Echo doesn't need the irony. Compare Ironic Echo Cut when something like this happens straight away as a cut to another scene.

Examples of Gag Echo include:

Film

Sin City gives us a couple since several characters drop the word "yeesh" whenever something happens to Jackie Boy. Dwight says it when he lands on one of Miho's shurikens, Gail says it when he and his men get sliced up and one of the Irish mercenaries says it when they find him in the car.
From Mean Girls when the Plastics find Damian's picture in the yearbook.

Cady: He's almost too gay to function
Regina: That's funny, put that in there.
Cady: (thinking) Oh, maybe that was only okay when Janis said it?
And when Damian finds it.
Damian: Too gay to function!?
Janis: That's only okay when I say it!

In Pirates of the Caribbean when Elizabeth ends up rowing herself to the island without any help, she mutters "Bloody pirates". Later we have this exchange:

Pintel: Hey, they're stealing our ship.
Ragetti: Bloody pirates!

Live Action TV

From the hurricane episode of Miami 7

Jo: The only way we'll get wind here is if Bradley has Cuban food
And later on.
Howard: The only wind we'll have to worry about is if Marvin has Cuban food.
Bradley: (To Marvin) You too?

A season 5 Sabrina the Teenage Witch episode has Sabrina cast a spell to make herself zip through her day at top speed. When she zooms down the college hallway, past her Aunt Zelda she says "that blur looks strangely familiar". When she zooms in and out of the coffee house, past her aunt Hilda, she says the same thing.
The 8 Simple Rules episode "Secrets" makes a Running Gag out of the family lying about who's on the phone, saying it's someone selling long distance. Then someone selling long distance actually calls. Also Rory gets punched in the face by a girl and lies, saying he walked into a locker. Principal Gibb gets punched by Jim and says he walked into a locker too.
- Another episode has Bridget suggesting that teachers and senior students get valet parking with the Driver's Ed students doing the parking. Later in the episode has Cate listing reasons to start working at the school and finishes off with "I heard a rumour they're going to get valet parking".
In Buffy the Vampire Slayer "Once More With Feeling" during the "I'll Never Tell" number Xander sings "[Anya's] toes are kind of hairy" and Anya sings "his eyes are beady". In the next scene when ranting about the situation both of them shout at the same time "my eyes are not beady"/"my toes aren't hairy".
In an episode of What I Like About You Lauren embarrasses Val at a meeting by saying that the woman on her magazine cover looks cross eyed. Later when Val finds Lauren's mug shot and shows it to her she says "does the woman in this photo look like she's cross eyed?".
The episode of Saved by the Bell where they find the school's old radio station gives us two. When the newspaper reviews the radio show Lisa worries "what if they don't like my outfits?" (despite being the radio) and when she reads the review it says "Lisa is an entertaining reporter and a classy dresser". Slater is awful on the radio and the gang are wondering how they tell him and Screech suggests "wave a skunk in front of his nose". Guess what the review says about Slater.
The Angel episode "Lonely Hearts" makes a Running Gag out of people not knowing what the logo on the Angel Investigations business card is (it's meant to be an angel). When Angel hands Kate a card at the end of the episode she says "What is this? A duck?

Western Animation

The Rugrats episode "Legend of Satchmo" has the babies scared of Sasquatch but mangling the name up as Satchmo. When Stu finds them:

Angelica: We were running from the Satchmo
Stu: Satchmo? The trumpet player?
Angelica: No, the monster.
Later when Grandpa finds them
Stu: They were afraid of the Satchmo
Grandpa: Satchmo? The trumpet player?
Stu: No, the monster.

- Also from "Angelica The Magnificent" when the babies think Lil was turned into a butterfly and ask her about it she says "you guys have been watching too many cartoons". When Angelica asks her about it, Drew replies "Angelica, you've been watching too many cartoons".
The Weekenders has Lor deciding to set Tino up with a girl called Dot Cardigan "because she looks just like him, but a girl". When Tino sees a picture of her...

Tino: "Hey, Dot Cardigan. She looks just like me, but a girl".