describes the rhythm of buttocks in motion, esp. desirable ones.
"tock" is short for BUTT-tocks.
"tick-tock" is also onomatapoeic, describing the sound made by shoes or high heels.
here's how it might be used in conversation:
George W. Bush: "tick-tock, twelve-o-clock." (the girl walking right in front of us has a fantastic ass i can't stop looking at. are you looking at it too?)
Dick Cheney: "tick TOCK." (yes, i see. it is quite remarkable)
George W. Bush: "tick-tock you don't stop" (i could look at that ass forever)
Dick Cheney: "you know what time it is." (i agree wholeheartedly)
George W. Bush: "tick...tock...tick...tock"
Dick Cheney: "hmmmm... tick-tock, three o'clock." (look to your right)
George W. Bush: "tick TOCK."