Maybe it isn’t obvious (either because you missed it or because it’s just a bad joke, I don’t know), but this post is a joke. I asked GPT-4 to explain it in a neutral tone for added hilarity:

The joke in the meme is based on visual irony. The question “Who even uses Celsius?” is asked, implying that the use of Celsius is rare or uncommon. The subsequent image of the world map in response, with only the United States colored orange (representing Fahrenheit users), humorously contradicts the initial question, highlighting that it’s actually Fahrenheit that is less commonly used worldwide, not Celsius. This undercuts the original question with an unexpected twist, which is the essence of the joke.