James Joule and James Watt were having a drink together and talking about their research. Joule said to Watt,
“Oh, here are my wife and children, come over and meet them.”

Come and meet the Joule family
“I’m sorry,” replies Watt, hastily retreating, “but I can only cope with one Joule per second!”
Of course, if your audience is at a slightly more advanced physics level, you could torment them with a similar joke about Ampere and Coulomb getting together in a Parisian Cafe, and Ampere running away from meeting Coulomb’s family because… he can only manage one Coulomb per second.
There are other variations, but I’ll leave that for you to take care of.
And then there’s Brahmagupta, the Ancient Indian astronomer and mathematician – the only scientist whose main claim to fame is that he discovered nothing!

It’s a Pauling!
Oh well, after that ‘a pauling’ joke, where can I turn to next? Perhaps Léon Foucault? But then he gave up on his work too – he was fed up of it going round in circles.
And finally, don’t forget the old, old joke about Nicolaus Copernicus… whose mom kept telling him that he’d learn soon enough that the world didn’t revolve around him!
Think you can do better (while keeping it clean)? Get typing!
The Joule-Watt relation:
The duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom = 1 Joule/Watt
I was going to tell the one about the physicist, the Van der Graaf Generator and the Superglue… but then I noticed you said to keep it clean. 😛
Ha ha! I’ll be telling this everywhere.
I know right