A slang term to describe two homosexual men. Derived from the sound made if two blokes could do each other at the same time, thus making their knackers (balls) "clack" against each other.
Julian and his boyfriend Richard were trying a new position that would enable them to shaft each other at the same time when their knackers started clacking. Their friend Steve, watching, cried "What a pair of knacker clackers!"
by Wayne Rooney April 26, 2007
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