An acronym that stands for "What The Fuck Would Jesus Do?", popularized by the blog Going Jesus (goingjesus.com) which emblazons the phrase on its t-shirts and stickers.
Sara got an email about her blog from some guy in Australia that went, "I am a born again Christian and blah blah blah saying Fuck all the time and blah blah blah WTFWJD and blah blah blah you're not a Christian and you don't have a relationship with Christ and blah blah blah."