What's the silliest thing you need to frequently look up?

Noticed today I _still_ don't remember what the middle argument for a three-part `for` loop is meant to be, and I look it up every single time. I'm a strong programmer with almost 30 years of experience, most of which is in languages that have `for` loops.

What do you still look up, or what useful mnemonic do you have? I stopped having to lookup argument order for `ln` after someone pointed out it was the same as `cp`.