So what are people laughing about? Since Overwatch went public (beta in 2015) people started uploading their experience to the internet. The most popular type of videos were PotG videos, also Play of the Game videos, also game highlights. As any good content is quickly gone viral and people started exploiting the framework of the PotG to transfer it into real life situations, for example:
Hanzo PotG parody by IGN
Pharah PotG meme by redrancor
Game of Thrones PotG parody
If you have just got an idea to make your own parody – check this article about the font used in PotG videos.