An Anti Clown is someone that will suck the joy out of any postive atmosphere, they will 'rinse' a joke or word until that word is no longer used amongst normal citiziens other than Anti Clowns. You can use a Anti Clown to make everyone leave your house if your having a unorthorized party and your parents come home. And they always have sister that people want to bang..
"Hey my mum had a baby on the weekend
"- Oh cool, dont tell Euan that Anti Clown the baby might die!