The very fine bit on a grater, ostensibly for zesting citrus fruit.
Utterly pointless. It all gets gunked up and I have to spend 10 minutes ungunking it with a pointy knife. Just use a hand-held zester.
I also fail to understand the point of oiling and lining a cake tin with parchment. Won't the parchment just do the job anyway?
What irks you?