What is the sneakiest thing you did to get back at an awful neighbor? Did you get caught?

Two stories. Neither of which involved me, and both of which may be considered only peripherally connected to the question. But here goes anyway:

A company (that I will not name) occupied one or more sections in a long, continuous building made up of a large number of identical sections.

They had a meeting room on the first floor (second floor for Americans), immediately below the roof void/loft.

A planning meeting was taking place when the site engineer/maintenance man came into the room and whispered to the managing director to say nothing, but come with him.

The engineer took the director up into the roof void and showed him a microphone hidden directly above the meeting room. A hidden cable ran from the microphone to the wall separating their section(s) from the next, where it disappeared through a tiny hole.

Assuming that the cable terminated in section occupied by a competitor company, the directors later held a series of fake meetings, in which misleading information was discussed. After they felt they had done enough of that, the engineer separated the two leads within the cable, and "tested" it by applying mains (240 volts) voltage. Some time after that, the cable fell away from the wall, apparently having been cut on the other side.

A car maintenance and repair company had a site that was on the outside corner of a right angle bend in a road, so that even though it occupied a large site, it only had a small entrance. At some time a car appeared parked close to the entrance, so that while not actually blocking it, made it very difficult for customers and the mechanics to get their vehicles in or out. The car was moved away, but then started re-appearing frequently in a similar position.

No one ever saw the driver, so the mechanics left notices under the windscreen wipers, asking the driver or owner not to park there. It made no difference, so they measured the car, and the distances between various fixed items in the street, and used wheeled jacks, similar to this:

to move the car out of their way to between a street lighting pillar and some other item (fore and aft), where it fitted with only about an inch to spare.

The car remained there for a few days, then disappeared for good.