Most likely one of the programmers was a fan of Monty Python, or perhaps one of the other older references to being hit by a fish. It wasn’t the only action command, just a weird one that lives on.

Here’s an interesting dive into the idea of action commands and how they’ve evolved into things like emojis and netspeak common today.

It was a Monty Python reference and common IRC joke.

I would make bots that would just go around and slap random people with fish lol

I also wrote a contextual menu that was nothing but scripts for slapping the selected user with a wide variety of fish.

12 year old me was a fucking dork.

Man that takes me back. Trout slapping was a huge thing on IRC in the 90’s. I never understood why.

Edit: Apparently from Monty Python. Of course.

Why wouldn’t it have