It's not common, or even used at all as a slur nowadays. People assume it's a racial slur against Asians, sense in WWII, the US often depicted the Japanese as animals in their propaganda. Rats seemingly became common because of the tagline "Trap the Jap", and because Asian caricatures are often depicted with large teeth.Rat is a racial slur against Asians? Is this common? I don't think I have ever heard of it. Some regional thing this snowflake thinks everyone knows about?
Wait a Minute, where are those tweets?
More proof that furries are just serial killers in masks.
That is so fucking ridiculous I'm leaning towards "OP had a friend send that DM as a joke", but if this was just manufactured for a joke tweet I don't know how anyone would ever come up with that shit without being a true believer in that crazy tumblrite mentality.