According to Roger Ebert, those mimes in Blow-Up are students: "These figures were described as 'white-faced clowns' in Pauline Kael's pan of the film, but a British audience would have known they were participating in the ritual known as 'rag,' in which students dress up and roar around town raising money for charity." The only definition I could find on the web is from WordNet. Rag week: a week at British universities during which side-shows and processions of floats are organized to raise money for charities. In his script, Antonioni simply writes: "A group of shouting students dressed in bizarre clothes and with white powdered faces are loaded in a jeep which drives into a paved courtyard surrounded by modern buildings."