I Like Pie
Fish gotta swim, birds gotta fly, all of the Cappers gotta like pie. It's a law of nature. This all started back in the old Caption This! days, when a Capper by the name of Joystick started a club called the ILPA, or the I Like Pie Association. The only requirement for membership was that you like pie, and who doesn't like pie?
Since then, 'I Like Pie' has become the standard catch-all response for nearly every poll on the Cappers Yahoo Group. Even if none of the choices in a poll appeal to you, you can always choose 'I Like Pie'.
Aside from polls and the ol' days of Caption This!, there's also a possible origin in an old, old song - very old, Britney Spears had nothing to do with it - from Episode #913 of the bygone puppet-show, to be found and listened to, in a copy of the web content SCIFI.com used to host here ( http://www.castleforrester.com/mst3k/freebees/#delta ). The meme also surfaced as early as MST3k #821 Time Chasers (1997), as seen around the 4:50 mark of this video, and showed up again in the When Loving Lovers Love song in the following episode.
In South Park: Bigger, Longer, and Uncut (1999), Cartman suggests adding 'Punch and Pie' to their message about the meeting of their resistance group, saying that more people will come if they think there will be punch and pie. Since then, the notion that pie can entice virtually anyone to do virtually anything has become yet another aspect of the running gag.
In episode 7 of The Flight of the Conchords (2007), the Conchords' manager Murray uses song to express feelings too deep to be spoken in conversation. Naturally, "I like pie" is amongst them.