Potato wank first came up on meme with links to this Tumblr post by IfIWereLoki, who said they would stop calling Scott from Teen Wolf a potato because it refers to a person with Down syndrome. The ensuing discussion included mention of the rather definitely ableist "I can count to potato!" meme, as well as a Scott-stan imploring, “it is rude, especially since the fans of the character have asked that the term not be used… So, this Scott fan asks that people please stop.”

The subject came up again about two weeks later. As the OP explained, many Teen Wolf fans on Tumblr

like to refer to the show's protagonist, Scott, as a potato. It's a thing. I assume it's to do with the fact that a lot of Teen Wolf fans see Scott as being kind of dumb. Today, though, I've seen a lot of talk on my dash about how 'potato' is an ableist slur, and calling Scott a potato is ableist.

“I can count to potato!” was brought up again:

That meme also seems like much more a Reddit/FB/Funnyjunk type thing; Tumblr has some intersections with those communities certainly but when someone calls so-and-so a potato/charming potato /weary potato they are not making a joke about Scott, or Channing Tatum, or T.E. Lawrence, having a learning disability. Either someone's seriously confused because they've seen the ableist use of “i can count to potato lol” first and thought that's what was going on with Teen Wolf fans, or someone really hates that nickname for their own reasons and is reaching for SJW outrage.

Another nonny wrote, “I thought it was because Scott's face is shaped like a potato, tbh.”

This thread also featured a probable Poe SJW troll linking to essays on FWD and elsewhere about derogatory terms for lack of intelligence being “ableist” and assuming everyone on meme was white. That spawned this thread, which is full of awesome and win.

Fast-forward three months. The issue exploded on a FanficRants post, which was dissected by Gentlefailers. Among the topics that came up were Mr. Potato-head, diana_molloy's wank history, a nonny ironically asterisking out the word as "p%%**%%%%**%%*o," an attempt to summon theo_harrison, snark about ffr, several video recs, this observation…

Huh.

I've been floored over the past few years watching this sort of thing ramp up and up, with the goalposts on what's a good enough response moved to ridiculous lengths, and it finally just hit me – this is all humiliation kink, from people who probably don't even know they have a humiliation kink.

…and, simply, "What a bunch of potatoes."

The very next post was titled Potato, Potatoe -FFA Post #182, and nonnies got right into the swing of things with a thread about the "Most offensive vegetables." (Later this would be countered with a "Favourite vegetables" thread.) Shortly thereafter came "seriously, potato? (an academic discourse)," which included a long thread about Derrida. Almost immediately there followed another tongue-in-cheek thread.

On page five of “Potato, Potatoe,” a nonny linked to the Tumblr blog Potato Justice. It is not known at this time whether the owner of this blog is a Gentlefailer. During an unrelated thread in the same post about gender-nonbinary Tumblr users freaking out over a '90s Nickelodeon meme, one nonny suggests, “We should start ranking SJ wanks according to the number of potatoes.”

Later in the same thread, there is explanation of the post title for the young'uns/non-USians. And then there was this, which boils down either to a square-off between two Gentlefailer trolls on Tumblr, or one Gentlefailer troll and one very very earnest teenager.