To waste time. A cute way of saying "fuck around." Combination of "circum-" meaning "around" as in "circumnavigate" and "fornicate," to fuck. Usually good for a puzzled experssion followed by a chuckle the first time someone hears it. Akin to circumflatulate, but harsher and harder to explain in polite company.
Would you idiots quit circumfornicating and get back to work?