The humor comes from the mismatch between the detailed setup and the nonsensical punchline.
It is believed to stem from a (possibly Uchi no Kaisha no Chiisai Senpai no Hanashi or a similar “small vs. large” gag series). In the scene, an older sister is exasperated because her younger brother has grown absurdly tall or broad – “maji de dekai” – but despite his intimidating size, he still acts childish or fails to notice that something is “hot” (literally, like a hot stove or metaphorically, an attractive situation). uchi no otouto maji de dekain dakedo mi ni kona hot
This is similar to the famous meme "Omae wa mou shindeiru" (You are already dead) but more chaotic. Where that phrase is cool and decisive, uchi no otouto... hot is flustered and contradictory. The humor comes from the mismatch between the
Fast-paced jokes and short panels cater perfectly to mobile readers with short attention spans. In the scene, an older sister is exasperated