>>37359
I don't think it was ever explained. There are definitely a few celebrity titans IIRC, but the one that really stands out to me is the "Aoi Oni" Titan. That was both a hilarious reference, a hilarious inclusion in and of itself, and, I think, clear evidence that the faces of the titans is meant to be a meaningless joke.

But yeah, you are right that this meta-joke ruins the tone of the series. It is odd, to make such jokes, in the midst of such seriousness, but yeah, I somehow like it just the way it is.