I pronounce it "mehm". I was in french immersion at a young age, so the first time I saw the word it was pronounced that way and it kinda stuck. The french definition of the word "meme" means "same".
I assumed things we called memes, because the same thing would be repeated over and over again until it finally stuck.
I mean, the english definition is about shared culture right? I assumed that since culture is repeated in order for it to be passed down, that the origin of the word itself meant "repetition" from the french language.