The “rule” is just “if you visit here you must post”. Putting “rule” in the title means “i’m following the rule”. The rule was never enforced, it’s really just a memes forum with less judgement re: meme quality (they have to post SOMETHING to satisfy the rule, being a dick in the comments is working against the “rule”).
Really just a way to say “post memes, be nice” without giving all the “YOU can’t tell ME to be nice! I will be mean just to spite you!” people their beloved raging troll erections.