Not necessarily dumb, but I had a harlequin rasbora that loved to lay down on anubias leaves. Like, fully horizontal. I can’t tell you how many times I thought it was dead and went to remove it, only for it to swim off when I got close with the net.

It wasn’t sick. It didn’t have any swim bladder issues. The little jerk just spent years pranking me for seemingly no reason.

Still one of my favorite fish.