Half-functional shower drains. The main shower in my house doubles as a bath, so the drain comes with a tab that plugs/unplugs as you wish. For some reason, the tab sometimes decides to stay in the middle (up for plugged, down for open) so water enters the shower faster than it can drain. So by the end, I'm showering with water up to my ankles. Of course this isn't the worst thing in the world, but it irritates me so much for some reason.