Currently rule_34 is an invalid tag, a move made after a post 6 years ago (forum #21433). The argument made was that Rule 34 denotes use of ANY commercial character, therefore it would just be a redundancy today to tag every Zootopia, Pokemon, MLP, etc post with rule_34 and it would lose it's meaning.
What I'm purposing is that we don't use rule_34 for EVERY commercial character, instead only for the ones that truly match the meaning behind rule 34.
Everyone seems to have a different definition of what Rule 34 is, with the most widely accepted phrase being "If it exists, there is porn of it." This more or less conveys surprise. Nobody is surprised to see another Zooptopia post (which has almost 300 pages of results) or MLP (which has 750+ pages) or pokemon (which also has 750+ pages), etc.
What is surprising enough to qualify as Rule 34?
Some random examples - The Geico character (8 results), Rango (20 results), Tony the Tiger (120 results), Bolt (200 results), etc.
So how can we define what should or shouldn't be tagged as rule_34?
Easy. The character needs to meet two conditions - First is obvious, they need to hold some popularity in pop culture (a widely-known mascot, character in a Hollywood movie, commercial entity, etc). Second, they need to be under the max submission threshold. Characters with more than 500/1000/5000 results (or say, 10/50/100/etc pages) would no longer classify as being rule_34.
It's not that complicated, and the rule_34 tag would bring up surprising results that'll make you think, "Huh, there really is porn of everything"
Updated by kamimatsu