Get a Hold of Yourself, Man!/Western Animation

In the season 1 finale of DuckTales (2017), Magica De Spell tries to get Scrooge to drink poison. Eventually she realizes his mopey state is not an act and she can't consider such a pathetic creature to be her arch nemesis, so she slaps him and tries to boost his spirits so he's worth defeating.
In one episode of SpongeBob SquarePants, Squidward has just traveled through time and met Spongetron/Future SpongeBob and his hundreds of clones. Trying to process what has just happened, Squidward curls up in the fetal position and intones "Future! Future!" over and over again until Future SpongeBob drops a brick on his head.
- In another case, SpongeBob begins "spiraling" after coming to the realizationt that he apparently is ugly, causing Patrick to slap him across the face. SpongeBob immediately calms down. Being The Ditz, Patrick raises his hand to give him another.
Done deliberately over the top, word for word, in Avatar: The Last Airbender, episode "The Drill". The added irony is that the man freaking out is the general in charge of defending the city's outer wall, and it is Sokka who slaps him...a teenager who is usually the comic relief character.
On The Fairly OddParents, when Timmy's old Crimson Chin action figure is mortally wounded, he says ("You're... you're... you're... *SLAP* You're my best friend!")
Stroker and Hoop:

Hoop: You can't slap a woman! (slaps Stroker)
Stroker: It was a regain-your-composure slap. They do it in movies all the time. (slaps Hoop)

Hilarity Ensues.

Parodied in the Family Guy episode "Breaking Out Is Hard to Do": The family are on the lam after helping Lois escape from prison. After Meg (calmly) wonders out loud where they're going, Peter slaps her and barks at her to calm down.
- Also done in the episode "He's Too Sexy for His Fat": Brian begins freaking out when he's covered in fleas, and Peter, quoting the trope name, immediately slaps...Lois. She's (understandably) less than pleased.
- And done to Stewie in another episode. The scene being a parody of Airplane! (complete with word-for-word dialogue from that film), Stewie won't calm down and a line of people with increasingly extreme methods is waiting for their turn.
On Camp Lazlo, Hypercompetent Sidekick Slinkman frequently has to do this to his brainless boss Lumpus --- and Lumpus is perfectly aware of this. They even have a frying pan reserved specifically for Slinkman to beat him with.
In Batman: The Animated Series, "The Demon's Quest (part 2)", Ra's al-Ghul has gone batshit insane and tries to kill his beautiful daughter. After Batman rescues her once, she says she can handle it and just slaps her dad upside the head. It works.
In Cow and Chicken, Cow at one point slaps a panicking Chicken across the face with her udder and tells him to snap out of it.
In one episode of Back at the Barnyard, Otis has a breakdown after a flying accident which he claims nearly killed all of his friends. When trying to snap him out of it, Freddie grabs Peck and smacks him a few times. Peck suggests he should have done the same to Otis, to which Freddie replies "He's much too big."
In the Buzz Lightyear of Star Command episode "Star Smasher", the LGMs are panic stricken and their Hive Mind is causing all of them to panic. Buzz splashes one with cold water and they all calm down.
Used on The Simpsons. When Ned Flanders panics about being lost at sea, Homer slaps him, calming him down... then keeps slapping him.

Bart: Dad! I think he gets the point!
Homer: (slap) Better (slap) to be (slap) safe (slap) than (slap) sorry (slap)'... sorry.
Ned: Diddly (slap)

- In an earlier episode, Bart ends up hitting a fellow soldier (It Makes Sense in Context) to get him to focus on the task at hand. Grampa later tells Bart off for it.
In the Ren and Stimpy episode My Shiny Friend, Stimpy's obsessive teleholic nature becomes too much for Ren, so the chihuahua smashes the T.V. causing Stimpy to freak out and break down in tears as the cat tries to put the T.V. back together. Ren then slaps Stimpy across the cheek and yells "Snap out of it!"
- Also, Ren uses exactly the trope's wording for this in "Rubber Nipple Salesmen", when Stimpy begs to talk at the next door they visit.
  - In "Royal Canadian Kilted Yaksmen" one of the duo's yaks is driven to a psychotic breakdown by Stimpy singing the Kilted Yaksmen anthem once too many. Ren is forced to slap the yak and yell "Come to your SENSES, man! This is no time for hysterics!"
In the South Park episode "Two Guys Naked in a Hot Tub", Butters goes into hysterics over being shot at by the ATF. Stan slaps him and even says the accompanying phrase, causing Butters to ask, "How come you slapped my face, Stan, huh? Why on earth would you do that, anyways?"
- Also exploited by Cartman, in "Jared Has Aides", after Butters points out Cartman's weight, he smacks him one, before quickly quoting the trope name.
Done to Bender by Fry in Futurama.

Bender: I don't know, Fry. For the first time in my life I feel like I've stolen enough.
Fry: (slaps him) Bender, snap out of it!
Bender: Sorry, I don't know what came over me. Let's go! (singing) I love stealing, I love taking things!

Hey Arnold!: Phoebe does this to Helga in the episode "Ms. Perfect" when Helga starts getting hysterical when upset over Lila's situation.
The Kids Next Door: When Chad (Numbuh 274) sends the Moon Base hurtling toward the sun, Numbuh 86 starts to panic. "What are we go'na do!!" To snap her out of her hysteria, Numbuh 1 slaps her.
Subverted in the Pasila episode "Salaviina", when Kyösti Pöysti is getting hysterical over the lack of alcoholic drinks in the entire Finland and the knowledge he won't be able to get drunk that Friday.

Pöysti: When will it be possible again? When? Tell me! When will it be possible again!
Repomies: Let go of me!
Pöysti: Tell me!
Repomies: I don't know! Now get a hold of yourself, Pöysti! (slap)
Pöysti: Ow! You hit me. Why?
Repomies: Because I can't drink either! God damn it!" (breaks down and sprawls crying on the floor)

Skipper from The Penguins of Madagascar does this to his men about every other episode.
In The Oblongs, Pickles takes advantage when her old high school friend Pristine panics and continues slapping her even after Pristine thanks her for calming her down and assures her she's alright now.

Pickles: I'll tell you when you're alright! (slap)

- Pickles slaps her again about a minute later.
In one episode of The Cleveland Show. Cleveland winds up gambling away all of Roberta's college money at a casino and goes to tell Donna. Donna ends up in a loop of surprised statements till Kendra slaps her to snap her out of it. Of course since Donna is a Sassy Black Woman...

Donna (After being slapped): Thanks Kendra, but do that again and I'll smack the taste out your mouth!
Kendra: Not the taste!

In an episode of Bobby's World, he learns karate but gets a power trip when he uses it. Towards the end, for some reason, he keeps telling his friend Jackie to hit him (perhaps as a demonstration), she finally does sucker punch him when he stops asking and his guard is down to show him what he's doing to other people, even though it seems almost like a Broken Aesop because he ASKED her to hit him for almost a minute before that scene.
In the episode "The Prank" from The Amazing World of Gumball, Darwin starts smacking Gumball in an attempt to get him to stop hyperventilating with panic. Gumball tells him that it isn't really helping, so Darwin switches to using a Cooldown Hug and comforting words instead.
In the Phineas and Ferb episode "Phineas and Ferb Interrupted", Phineas and Ferb are made dullards by a stray shot from Dr. Doofenshmirtz's Dull-and-Boring-inator. When Buford starts to succumb to their literally mind-numbing prattle about meteorology, Isabella slaps him out of it.
In My Little Pony: Friendship Is Magic, episode "Lesson Zero", Spike yells at the stressing Twilight Sparkle to "snap out of it" while physically popping her thought bubble.