A leisure pastime, mentioned in Making Money, which is wrapped in mystery and enigma. What it actually is remains undescribed, but we have Vetinari's word for it that this is a dangerous and potentially lethal leisure activity. At some point in the book, Moist was encountered with a lock he could have opened with a sneeze. Hmmm...
This pastime was taken up by Moist von Lipwig when the Post Office started to get boring and routine and presented fewer and fewer challenges, apart from getting through a staff pensions' committee meeting without falling asleep. Moist has also started edificeering, a sure sign to the Patrician that he will be receptive to another life-threatening challenge causing him to hone and refine his skills. Especially since edificeering, to a con-man, involves the additional challenge of out-thinking burly vigilantes with a direct and forthright attitude to dealing with what they presume to be an unlicensed thief.
Vetinari noted that Moist's need to participate in dangerous sports, where one wrong move could see him horribly maimed or even dead, seemed to go away whenever Adora Belle Dearheart was in town. He implied there was a correlation between these two observations.
On Roundworld, particularly in Great Britain, there may be two referents which shed more light on this enigmatic practice. There is the Oxford University Dangerous Sports Club, which in the past has sponsored things such as (a) putting a grand piano on skis and sending it, as well as the attached pianist, down an Alpine ski-slope; and (b) firing people out of reproduction mediæval catapults, albeit in the rough and hopeful direction of a safety-net.
Secondly, only the British could come up with a sporting craze called Extreme Ironing. This involves lugging an ironing board, plus iron, plus token clothing item to be ironed, to an unlikely, remote, and ideally dangerous place, such as a wide ledge 1500 feet up the side of an otherwise inaccessible Scottish mountain or the very top of a construction crane. An associate then takes a photo of the clothing item being "ironed", as proof that the challenge has been completed..