The following amusing panel has been making the rounds for awhile now...
And luckily, thanks to helpful reader onion3000, I now have the original panel to share with you all as well as the context behind it! Enjoy!
The story is an "Imaginary Story" from 1965's World's Finest #153, by writer Edmond Hamilton and artists Curt Swan
The concept behind the story is that Bruce Wayne believes that Superboy was responsible for his father's death, so he became Batman specifically to fight against Superboy (and then, naturally, Superman).
Anyhow, the panel shows Batman's partner, Robin, taking issue a bit with the Superman obsession (the panel, as you can see, was reversed for greater comedic effect).
onion3000 also shared with us the aftermath of the slap, as Batman comes up with a way to make everything "all better"...
Thanks again for all the scans, onion3000! Good stuff.