@shachadira r/woooosh
Since the joke went over your head, lemme explain it.
Apparently in Japan, all forms of public display affection is frowned upon, which mindbogglingly extends to
handholding.
So the anime community decides to poke fun at it, by equating handholding to something even lewder than sex. Then it became a meme, and the rest is history.
TLDR; spread the meme, for the lulz.