A British equivalent of ‘that's what she said’ is ‘as the actress said to the bishop’.

The phrase far predates The Office, but was often used by Ricky Gervais’s character David Brent in the original British version of the show. When the sitcom was brought overseas and adapted for American viewership, Gervais’s expression was translated to “that’s what she said”! This idiom, spoken by Steve Carell’s Michael Scott, quickly became the show’s catchphrase and an American pop culture phenomenon.