A weeb is someone who’s not Japanese, but is obsessed with Japanese culture and uses Japanese words in chats, etc. as if everyone knows what they mean or because they want people to think they’re Japanese. In this case, they’re talking about a weeb who’s also obsessed with the sexual side of Japanese (web) culture.

...or sex in general

https://en.wikipedia.org/wiki/Japanophilia#21st_century
Здесь это, правда, weeaboo

WEEB is a shortened version meant to sound like dweeb