You’re presuming most people regard text on a selfie as a meme.

I’m convinced the majority of people think a meme is a recurring image format with humerous intent (more or less).

For what its worth, I’m of the opinion that words are not prescribed, words are defined by their use.

This may seem contradictory, until you realise that you can’t just let every definition of a word be equal and valid.

If my definition of a meme was a blue towel, which was shared by ten other people, then asking you to fetch my meme (blue towel) is moronic.