Rattata is iconic in the sense that it is one of the first Pokemon you ever meet in its debut generation, and it stands out because of that. It's not liked by everyone, sure, but most people know its name and it's very recognizable because both it and Pidgey stand out as two of the first Pokemon who show themselves in the game in the first route. It does have some meme value among more passionate fans too. Pidgey is arguably more iconic, and people actually like Pidgeot, but Rattata is certainly recognizable. Almost everything in the early game of RBY is recognizable and well known in the greater public consciousness. This also includes Spearow, Caterpie, and Weedle, along with their respective evolutions.
Rattata is well known in the same sense that Zubat and Tentacool are well known in a way. It and Pidgey are in just about every field route in RBY, at least one of them, much like how Geodude and Zubat are near constants in caves and Tentacool is everywhere while you surf on water routes. Which has made them distinctly recognizable in the public consciousness as "common and annoying wild spawns".
There are different categories of recognizable Pokemon among the original 151 I feel. There's the distinctly iconic and marketable ones, which are the three starter lines (Charizard most of all), Pikachu, Eevee, Lapras, Snorlax, the three legendary birds, Dragonite, Mewtwo, and Mew to name a few, and then there's stuff that's common in the game that everyone at least knows the name of, like Rattata, Zubat, Pidgey, etc. And Onix, since it's the very first boss fight in the game.
Almost everything in the beginning part of the Kanto dex is recognizable, including the bugs, Pidgey, Rattata, and Spearow, as is the stuff towards the end, like the legendaries, Dragonite, Snorlax, the fossils, Ditto, and Magikarp+Gyarados. It's the stuff in the middle of the dex that tends to be obscure. Stuff like Goldeen and Doduo.
As for Rattata, it and Pidgey are the weird kind of Pokemon that inspired Pokemon who were made in their image and they repeated that "archetype" for every game for each new roster of Pokemon. Rattata has a lot of expies, and basically at least one per new generation: Sentret, Zigzagoon, Bidoof, Patrat, Bunnelby, Yungoos and Alolan Rattata, Skwovet and Wooloo, and last but not least Lechonk. Whereas Zubat and Tentacool largely kept reprising their classic roles game after game.
