Mr Carpenter said characters such as Pennywise, the murderous clown in Stephen King's novel It, and the evil criminal mastermind the Joker in Batman, had contributed to the view of clowns as "scary".

BBC: Scary clown mask

The movement started around the time of the 1992 riots that followed the Rodney King verdict, when a previously wayward young man named Thomas Johnson reinvented himself as Tommy the Clown and established an institution called Tommy's Hip Hop Clown Academy.

WSJ: Bothered and Bewildered

YouTube users around the world responded by posting a series of Bhumibol-bashing clips, portraying the king as a clown, as various types of animals and as a pedophile.

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