Basically kids were stuck in a flooded cave and a bunch of people wanted to save them including Elon.

So he sent a team of Tesla engineers and a mini submarine. The submarine was never used and instead a professional diver saved the kids.

The diver called the submarine a PR stunt and suggested that Elon "stick his submarine where it hurts" (admittedly not very nice).

Elon responded with a series of tweets including one where he called the diver a "pedo guy" (even less nice)

More info about it and the later deflamation court case: https://www.bbc.com/news/world-us-canada-50694074