The phrase you're swell comes from older American slang where swell meant excellent or wonderful, popular long before modern compliment slang. This short clip is shared online under the Friends name, reflecting how lines from the long-running sitcom continue to circulate as bite-size reactions long after the show ended in 2004. On soundboards and in short edits, the line survives because it is instantly understood, family friendly, and short enough to drop into a pause without explaining the joke or slowing down the scene that surrounds it.