It is a catchphrase associated with town guards from The Elder Scrolls V: Skyrim. It becomes popular (meme) in a such way similar to the other known "Took an arrow in the knee
", "Stop right there criminal scum!
" and the "FUS RO DAH
" meme. From the game, you can hear the dialogue when you interact with the NPC guards:
"You see those redguards from Hammerfell? They’ve got curved swords. Curved. Swords"
Hearing it over and over again, especially the last part where the NPCs emphasize the Curve Swords, makes it sounds funny yet somehow annoying to most players, until someone decided to troll over the internet using this sentence. Therefore being popular and well-known to the fellow internet users.
They used to take an arrow in the knee, but now they've got curved swords. Curved. Swords.