The line comes from Family Guy, the animated sitcom created by Seth MacFarlane, and is spoken by Peter Griffin, the show's loud and tactless lead character. Short reaction lines from the series have long been clipped and shared online, and this one spread as a soundboard and meme sound because it sums up complete disinterest in four seconds. It remains popular in edits and chats where a normal polite response would feel too weak, letting one familiar cartoon voice say the dismissive part out loud for everyone.
About this sound
Peter Griffin saying OMG, who the hell cares in Family Guy, a blunt dismissive reaction clip people use when something is boring or pointless.
This is Peter Griffin delivering the line OMG, who the hell cares with flat, annoyed exasperation, as if the topic in front of him is too trivial to deserve any attention. The delivery is the joke, starting like genuine surprise before dropping straight into total indifference. It cuts a conversation dead in a funny way because the reaction is far more rude and dramatic than the situation calls for. Viewers instantly read it as bored, unimpressed and done listening, which is why the clip works so well as a standalone reaction.