I once - on a very tired day admittedly - tried to put the kettle back into the fridge instead of the milk.
And once every few years I'll look for my sunglasses only to find them on my head.
But I think the most embarrassing was I'd just moved into an new apartment and there were a row of identical ones.
The doors all unlock with this automatic key thing, so it wasn't until I was standing in the middle of the hallway with a strange guy looking at me that I realised I was in the wrong apartment. He hadn't locked his door!