It could be worse.
One coworker was gleeful about his acts of hateful revenge.
1) A full bottle of Superglue in locks (office doors, car doors, house doors, equipment ignition switches).
2) Dropping tro and defacation on the glass doorway to the office he couldn’t get into because they went to a card reader entry and he didn’t have a card... and needed to use the restroom (obviously).
3) Fill up the underside of a car door handle or pickup tailgate latch with axlegrease.
There are many others... but one thing that he explained (with glee) was how when he was a juvenile delinquent and a neighbor pissed him off, he would buy a whole bale of peat moss and under cover of darkness, dump the whole thing in their pool... plugging up their filter and wrecking the filter pump... and it was a 2 week long affair to get rid of all the peat moss.