The word duck is an abbreviation of the term 'Silent Duck' which refers to the shape made by the hand during fisting, or initiation into fisting. Silent Duck

And so the term cheeky duck refers to slyly slipping a silent duck in during sex, aimed to catch the receiver off guard.
' Hey Freddie guess what?! '

' Woah what happened Sam?! '

' The other night i was having sex and Amy slipped a cheeky duck in! i havent shat right in 4 days! '
by s0a0m0 November 25, 2009
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