W

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"