I used to do tutoring when I was in school and this pun was actually great for helping students remember. They all hated it, and that's why they remembered it.
It's been a while since I learned about cations and anions, but I still remember their charges by thinking of anions as onions that need a single sharp blade to cut, making a "-" sign, while cations have 2 front paws of sharp claws that make a "+" sign. It's a dumb way of remembering that I came up with on the spot when I first learned about them, but I still remember after more than a decade.
