High value resistor wired from mains live to a pushbutton which connected it to earth.
High enough to not be dangerous but low enough to cause a nuisance trip whenever the button was pushed.
Drove a colleague insane for *months*
Same workshop, different colleague, they went on holiday so we got some really strong double sided adhesive tape and stuck down *everything* on his workbench.
Different workshop, in the PSU repair benches we had some basic high wattage resistor dummy loads in fan cooled metal cases that were used for testing, we did all sorts, 'Soundbomb' sirens hidden inside and wired across 12V load, a random chirping thing we found that sounded just like a PSU 'hiccuping', a 555 timer connected to a Piezo, free running high enough to sound like a PSU squeal
The worst/best, we were in an industrial unit which had 12ft high brick walls then a 'tin' roof another 10ft or more above.
Ideal position for a theatrical flash/smoke pot.