Biotic Baking Brigade

The Biotic Baking Brigade is a loose, international group of activists known for throwing pies at famous people, like Bill Gates, the Swedish king Carl Gustaf, or Monsanto's CEO Robert Shapiro. Members follow a left-wing philosophy, with members also active in ecology, social justice, gay rights, animal rights, and feminist movements. Throwing pies at people is supposed to ridicule and humanize them.

The group is also known as Pâtissiers sans Frontières (confectioners without borders), and they have mottos like "The Pie is the Limit", "Torte statt Worte", or "Speaking Pie to Power".

Fun fact: Wikipedia contains a list of well-known people who have been pied.