I'm not sure, but I find it's two runasin words and not a locution. Unless you want to say "kick in the ass" or similar. See Quechua/chaki ( "foot" ), quechua/siki ( "buttocks" ) .
It's two words from the Quechua language. Chaki means foot or paw and siki, means buttock. The two joined would mean buttock leg or lower buttock : Coxis , which in Quechua is called Siki tullu or siki sucks tullu . Siki ukutu means anus.