Very low fi and very childish too but years ago I once emptied all the paper bits from three large hole punchers into a colleague's coat pockets and I also undid his fold up umbrella and poured a load in there too.
The reason why??
I had returned from maternity leave a stone heavier and he shouted across the office "who ate all the pies".
I bided my time so he couldn't pin it on me and I did it when he was in a meeting. I also waited for a rainy day.
On the day I did it I left work around ten minutes after he did and as I turned the corner the heavens opened once again so I was delighted that he would need to use his umbrella for the walk to the station. As I pass tk max further down I saw a whole load of white dots scattered all over the pavement. I know its childish but it felt great knowing I'd showed him up on a really busy high st

He was fuming the next day and it really got to him that he couldn't get to the bottom of who did it and why. I even agreed with him when he said it was a juvenile thing to do to throw the scent off