What's a "mimi?"

Okay - I know MEME is pronounced "meem," but it would make the same amount of sense to me if it was pronounced "mimi." I don't understand what memes are, and even after my young co-workers sent me hundreds of them to pore over, I still don't get it.

Like, why are so many of them pictures of Gene Wilder as Willy Wonka? Or the Dos Equis guy? Or - is that Viggo Mortensen?!

I guess it's possible (and very likely) that I'm just too old to understand. Although I DO understand this one...