Usually only used in email/messaging/written form.
Replying to someone admitting to doing something incredibly stupid or makes a stupid comment.
Using only "W" as a reply is the same as rolling ones eyes or saying "your an idiot".
Or a shortened version of: "Your as stupid as George W Bush"
she: "I was so drunk last night that I forgot where I lived and it took 5 hours to walk home".
he: "W"
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