You could add a little tag beside their username saying whatever you wanted it to. It was great if you found someone to be particularly helpful or knowledgeable about something and then would see them pop up in other places. I remember tagging that guy who really knew vacuums for e.g.. Or maybe there's some other little quirk. I've forgotten the username of the dude who didn't want to shit for three days here on Lemmy and definitely would've tagged them as such.

Now that I think about it, I remember seeing how many times I'd upvoted people beside their name too (was that in the app or an RES thing?) which is another nice little feature.