In Girl Genius, the unnamed circus chef is fond of using his "calming pie" to calm down people by applying it to their faces. In a subversion, it doesn't usually work too well, as seen here.
In Juathuur, father figure Arvval slaps Faevv when he learns she strayed from the way. This allows him to influence her for... about ten minutes.
In El Goonish Shive, during the aftermath of the Painted Black arc, Grace is in a minor Heroic BSOD over her guilt of not being able to stop Damien when he first appeared, as well as failing to stop him from committing suicide in the final battle. She begins to wonder why she should have her powers when she couldn't even do what she was given them for (stopping Damien before he could kill anyone), and how when she did use her powers to stop Damien, she ended up becoming a mindless killing machine. Her "sister" eventually snaps her out of it via a verbal form of this.
In the the storyline, Melissa did this to herself when her delusions about Justin were getting out of control and even references Mythbusters involvement with this trope.
And Jade upgrades the Brightslap to a Brightbeatdown. Beware the Nice Ones indeed....
Laura in Collar 6 administers a much-needed love tap to her Mistress when Sixx indulges in a bit of Wangsting, followed by an equally-well-deserved verbal slap. It ultimately comes across as heartwarming.
Performed by DiDi on Zii when she considers sex (then a threesome) as a way of apologizing for breaking Gary's rare Transformer toy.
Just as well; It wasn't really broken, it was designed to pop back together. Though they had no way of knowing that at the time.
When Greg of Real Life Comics got into the 'zone' and lost his connection to reality. Dave tried to slap him out of it. It worked for a couple of seconds.
In Mokepon, Atticus is just recovering from nearly being shot when he and Dragonthing run into a giant swarm of angry Bug Pokémon. Dragonthing has to bite Atty to knock him out of his Heroic BSOD before they high-tail it.
Magellan: Used to get Charisma out of future shock