The joke that “on the Internet, nobody knows you’re a dog” no longer works
The joke comes from a famous New Yorker cartoon by Peter Steiner which was published in July 1993. It shows two dogs and a desk atop which sits a desktop computer. One dog is sitting on the office chair with two paws on the desk and is explaining Internet anonymity to his companion.
The date of publication is significant, because neither Google nor Facebook existed at the time and the protocols of the open Internet did indeed facilitate anonymity.
The cartoon wouldn’t make any sense today. In fact, a better version — based on Russian manipulation of social media in the 2016 Presidential election — might be: “On the Internet, nobody knows you’re a Russian”.
Wikipedia, “On the Internet, nobody knows you’re a dog”, https://en.wikipedia.org/wiki/On_the_Internet,_nobody_knows_you%27re_a_dog
Malcolm Collins, “The Ideology of Anonymity and Pseudonymity”, HuffPost, 2 October, 20913. https://www.huffingtonpost.com/malcolm-collins/online-anonymity_b_3695851.html