It started on Hallowe'en 2011, with a nonny venting annoyance at a PostSecret secret judging adults who don't cook. The discussion was initially calm, until one person said,
Cooking is following directions like dancing Odette in Swan Lake is following directions - you have to know what the directions mean, and you have to have the skills to execute them. A lot of "Cooking Is Easy!" people don't realize this because they had a parent who cooked a lot so they saw "chopping an onion" on a regular basis and know what that looks like even if they've never done it.
That sparked the incredulous question "How the living fuck could anyone not know how to chop an onion?", and shit was ON.
Possibly the lowest point in the wank was this: "Chopping vegetables is the kind of kitchen work I sometimes ask the people with a mild intellectual disability I work with to help me with..."
This wank has been commemorated with a mod icon. It comes up frequently as an inside joke, such as in this "Ask Me Anything" thread. (Fairly recent, as of this writing, example: this gifset, mentioned here.)
Chopped Onion Wank flared up again briefly in early June 2014when nonnies wanked about whether it was practical or not to chop onions using a blender.