The mid-air light-spank is a customary ritual of flirtation between two (or more) mammals of mating probability since fish first crawled from the ocean onto dry land. How the person who got smacked on the ass reacts differs, either with violence or embarrassed indifference.
This can be subject to some Values Dissonance when coming from older works, as nowadays it can be a form of sexual harassment.
This trope isn't just relegated to an open-palm. Variations like pinching and finger-brushing are included. Unlike Someone's Touching My Butt, the smack presented in this trope is usually done completely on purpose, though the tropes could be confused by the person who gets the smackin'.
Also note that it's not uncommon for guys to do this to each other in various male-dominated occupations like sports and the armed forces, displaying something between Gay Bravado and an implicit close trust between them. Or an attempt to establish dominance, depending on the people involved. In the US, this is known as a "Good Game." With increasing numbers of women serving in the armed forces, the acceptability of this practice has begun to come under scrutiny, for reasons mentioned above already.
- Empowered has the titular heroine repeatedly subjected to this by the superhero Phallik (wielder of the Mighty Phallospear,) with him justifying it as a gesture of "comradely affection". She gives him the benefit of the doubt at first, but as soon as it becomes obvious that he doesn't do this to anyone except her, and is just a sexist pervert taking advantage of her reputation as a helpless bondage-prone Damsel in Distress, she calls him out for it. It turns out this habit is so deeply ingrained into him that even after he's killed and comes back as a zombie, his reanimated corpse still tries to do it, and even when the corpse is out of the picture the semi-sentient spear can be charged up to its full destructive power when she slaps her own ass with it.
- In Chapter 9 of The Viking Samurai, Hiccup smacks Astrid's rear during their fight, mocking her efforts to capture him.
- In pretty much all of Mercaba's Evangelion fics, Shinji's paramours really seem to enjoy slapping his ass.
- Ladybug In A Half Shell: Johnny Smith (also known as "Johnny the Perv") is a student at April and Casey's school infamous for doing this. He has done it before with April (getting his tooth kicked out by her for his troubles), has been beaten up by Casey for doing it due to his Big Brother Instinct and got a severe Death Glare from Adrien when he tried something with Marinette.
- CRME: Roman does this to Cinder in Chapter 20 because they've had sex before and were keeping it from Emerald. She is shocked, but still reacts favorably to it. Even exchanging some flirtatious banter back.
- Toph does this to Princess Yue in Chapter 6 of Evil Fuzzy 9's Sokkarem Week 2016. She doesn't stop there, going further by spending a few minutes fondling it.
- During the Good-Times Montage in The Incredibles, Bob gives Helen a pat on the butt as he walks by her in the hallway, only to receive a pat right-back from across the hall.
- In Brave, Fergus does this to Elinor in the first scene just as Elinor is berating him on giving Merida her first bow, causing her to jump briefly in surprise.
- In ParaNorman: Alvin has a crush on Courtney during all the movie, when the characters stick together against the Angry Mob they decide to hold hands.
Courtney [reacting]: Hand, Alvin! My hand!
- When the Boisterous Bruiser Prince Vultan in Flash Gordon is near Dale Arden he pats her on the bottom, startling her.
- Baby Herman from Who Framed Roger Rabbit dispatches his nursemaid / handler with a smack on her ass, as well as sending her to get a racing form. Baby Herman does this in order to have a private and serious conversation with detective Eddie Valiant.
- In Goldfinger, James Bond does this to a woman giving him a massage after the titles after asking her to leave so he can talk shop with Felix Leiter.
- Bond does this to Tania in From Russia with Love. She responds in mock disapproval that there are some English customs she's not going to put up with.
- In Bull Durham, Crash does this to Nuke when the latter is trying on a pair of Annie's garters in the locker room before a game.
- Local hoodlum Johnny C from Flashdance both spanks and fondles Alex's derriere, because he thinks he can do as he pleases in Mawby's bar. Johnny C gets his drink poured in his lap as a comeuppance.
- The Way of the Gun: When Parker and Longbaugh enter the Mexican bordello with guns, the prostitutes all file out and Longbaugh gives one of them a smack on the rear as she passes by. This was ad-libbbed by Benicio del Toro. The actress was reportedly not at all pleased by his improvisation.
- Robot Jox has the "male-dominated sports/military" non-flirtatious variant, with one of the technicians helping Achilles prepare for battle giving him a smack on the ass before he enters his Humongous Mecha. Before the final fight, the same technician accidentally spots Athena when she reacts in shock to the same gesture after stealing Achilles's uniform to take his place in the match.
- Sucker Punch: During the Storming the Castle fantasy sequence, the girls stack up before going through a doorway (a practice used by police and military in Real Life before entering a potentially hostile room). Rather than signaling her readiness to go through the door with the customary tap on the shoulder, Rocket instead elects to give Sweet Pea a very tactical smack on the butt. Given that they're sisters, this probably fits under "close camaraderie" rather than "flirtatious."
- Mr. Theopolis in Fido does this to his zombie slave girl as "reward" for picking up the newspaper. He was forced into early retirement for fraternalize too much with female zombies.
- Done in the first sequel of Revenge of the Nerds; Nerds in Paradise by the manager of the Flamingo Hotel, Mr. Buzz to Sunni (the lead female character and Love Interest of The Hero) although more in the sexual harassment field than flirting, but that was the point.
- In the 1980 sci-fi parody Galaxina, Sergeant Thor tries to slap the titular Robot Girl on the ass and gets an electric shock.
- John Wick: Chapter 2. While patting John Wick down for weapons, the mute female Dragon checks his crotch, then reaches between his legs to grab Wick's ass.
- When the heroes in Everworld run into the Amazons, it's mentioned they play grab-ass with David and Christopher (Jalil having already been claimed by April, to his surprise).
- One part of CARDINAL's chain of couriers in The Cardinal of the Kremlin is a woman who meets with a man who comes up behind her so she can't identify him to make their hand off. They have been doing this for several years and lately, he has been making a number of amorous physical touches (such as gently pinching her rear end), making her wonder what kind of lover her mysterious contact would be.
- In Honor Harrington Paul does this to Honor while they are riding in an elevator. He manages to time it just before the elevator arrives so that she doesn't have time to get revenge before the doors open.
- The Leverage episode "The Bank Shot Job" opens with the team on a job targeting a corrupt judge who is introduced by slapping the rear of a young woman. Upon finding out she's nineteen, he jokingly asks if she has a younger sister.
- Game of Thrones:
- In "Second Sons" (season 3, episode 8), Queen Daenerys meets with three officers of Second Sons, mercenaries hired by Yunkai, and she tries to bribe them to her side. One of the captains makes lewd comments, says he and the Second Sons will all rape her and generally behaves like an asshole. When they leave the tent, he smacks Missandei on her butt.
- In season six finale, Walder Frey asks a serving girl, who is Arya Stark in a Faceless Men mask, if she's from his castle, to which she says no. Walder then remarks "You pretty," then smacks her in the bum.
- Whose Line Is It Anyway? has covered "Times when the athletic butt-slap is inappropriate." A couple highlights:
"Your Majesty." (butt-slap)
"How're those hemorrhoids?" (butt-slap, causing painful grimace)
- Star Trek
- Done by Charlie to his crush Yeoman Janice Rand in episode Charlie X of Star Trek: The Original Series, with a certain degree of innocence.
- The Grand Nagus of Ferenginar pinches Kira Nerys' rear in an episode of Star Trek: Deep Space Nine; Kira threatens to break all of his fingers if he does it again.
- Buffy the Vampire Slayer:
- In the first season, local bully Larry is practicing self-defense exercises with Buffy and she has to fake that he's stronger. He grabs her butt, prompting her to react with her super strength. Joke is, Larry is actually gay and he's out of the closet a couple of episodes later.
- Happens to Buffy again in the third season when she's working as waitress in L.A. The fact that she doesn't knock the offender across the room is part of the drama.
- Person of Interest. In "Bury the Lede", ruthless ex-CIA professional assassin John Reese is hilariously thrown when professional fixer Zoe Morgan gives him a smack on the ass as part of their ongoing Ship Tease.
- Get Smart. Maxwell Smart is talking to a Control agent disguised as a cabaret dancer, who tells Max to pinch her behind so it won't look suspicious as to why he's standing close to her. She then slaps Max, because reacting any other way would also be suspicious.
- In The Rock Cocks, Clover gives Coral a pinch on the butt.
Clover: Let me know if your cute butt needs a hand or two. [Clover pinches Coral.]
Coral: Hey! All right, Mrs. Grabby-Crabby!
- In Bob's Burgers, Tina watches how baseball players smack one another's asses to encourage one another. She then decides to become their water boy, so she can smack them on the asses as well. At one point she says that she is in love with all of them at the same time.
- Star vs. the Forces of Evil has Janna do this to Marco in "Bon-Bon the Birthday Clown".
- Kaeloo: One season 3 episode has Mr. Cat do this to Kaeloo. She, of course, gets angry and starts yelling at him.
- Slimer's Evil Twin spanks Janine in episode "Trading Face" of The Real Ghostbusters, prompting Janine to get suspicious of his identity.