This meme is chiefly an image-based meme that involves using a phrase along the lines of “So there’s this girl. She’s beautiful. She’s reading this right now.”
Although the origins of this phrase are murky, according to a submission on Know Your Meme (archived link), the phrase has been on the Internet since at least 2012. Early examples of the phrase seem to use it in a sincere fashion, but users in 2017 seem to have found a humorous or cringey quality in them and have used the phrase ironically.
(Note: It is difficult to determine how ironic the Instagram post is supposed to be, but all things considered, it seems to be genuine rather than ironic. For one thing, the account that posted the image seems to be a non-ironic fan account. In addition, it was posted in 2013, which was before memes about John Cena became popular.)
As noted in the Know Your Meme submission, joke versions of the phrase started becoming popular in 2017.
The meme has become popular on Tumblr around November 2017.