There actually is a generally accepted difference between otakus and weaboos among the Anime/Manga community, as far as I know. Otakus tend to be a bit more tame, they have a genuine interest in anime/manga much like any other media community, they tend to cosplay or do something with their love for it, but they don't let it absolutely consume their lives and personalities. Whereas weaboos are a lot more over the top and use anime/manga as an excuse to be REALLY WEIRD and sometimes even behave inappropriately towards other people when it comes to what they love.
It's like the difference between love and obsession IMO If you sat down and talked to an otaku about their favorite anime, they'd probably be like "Yeah, Naruto's pretty good, it has its good moments and its bad, but I can appreciate it for what it is." Meanwhile weaboos are like "NARUTO X HINATA 10/10/10/10 ME_IRL IF YOU DON'T AGREE WITH ME YOU'RE LITERALLY HITLER". Otakus are the community members whereas weaboos are the extremists that take it WAY too far.
How to tell if someone is a weaboo or an otaku? Are they absolutely annoying to talk to and make you want to kill yourself? Weaboo.