In the Discworld series of books there is a character named Lord Vetinari, who, in addition to being a large city’s ruler, owns a clock that ticks irregularly, but still keeps accurate time. In this series, he keeps the clock in his waiting room in order to unnerve people.
As I haven’t read the books, I’m not sure how effective this is thought to be, but perhaps one would assume that someone who is willing to “modify the flow of time” shouldn’t be trifled with. If you too would like to unnerve your friends and enemies as they patiently wait for you, this kit will allow you to build your own Vetinari clock. As seen in the video below, it ticks irregularly, but always averages out to the correct amount of time.
The kit comes with a circuit board and parts for you to solder onto a provided wall clock. If you’re not crazy about the clock provided, the movement mechanism looks like a standard model that you could find at a hobby shop or at various online outlets. You should be able to disassemble it and make your own custom body. On the other hand, the “ordinariness” of this clock might be an advantage, since your guests wouldn’t initially suspect anything!