One of my best friends was working as a section manager in a retail store. He bought a box of like, 400 rubber duckies off Amazon and started leaving a single one on his boss' desk at random times. Never said a word to her about it, and would pick odd times to do it to throw her off the scent - like if he came on an off day to shop, he'd sneak one in. He'd come in 30 mins before his shift started to do it. He'd stay late to do it.

He did this for *at least* six months before he got promoted and got a transfer. On his last day of work he walked into her office with the box of the rest and turned them upside down on her desk.

She hit something like a combo of hysterical laughter and sobbing - "OH MY GOD I THOUGHT I WAS GOING INSANE".