Improv Everywhere has launched Improv Everywhere Global. There's a Vancouver faction!
From wikipedia, "Improv Everywhere (abbreviated IE) is an unorthodox comedy group based in New York City, formed in 2001 by Charlie Todd. Its slogan is "We Cause Scenes," which the group lives up to by executing non-demeaning pranks in public places. The events ("missions") organized by the group are often considered flash mobs, but the group's website insists that they have nothing to do with flash mobbing and that IE was created years before flash mobbing gained popularity."