It's basically a dog whistle for the pedo cartoons.

The word is everywhere in weeb circles. I refuse to use it because if you're an adult you can just use the actual words when talking about sex.

"Lewd" is an oddly infantilizing euphemism, it's a word you'd use when talking about sex to someone who still giggles every time you say "penis", to whom sex is a naughty word. That's the vibe that that word gives me and why I don't like it.