The joke was (this was a couple years ago, that's an OLD pic) that Uzuki used to be completely ignored by Namco in favor of other girls getting SRs (see her wiki page for more details), so some fans came up with a "Uzuki is the resident Butt Monkey" meme that morphed into "dark/yandere Uzuki", a little ala dark Haruka.
But then Uzuki got more attention and more character development besides "ridiculously average girl", making the Shimamura-san pity meme fade away.
fun fact I used to DESPISE Uzuki bc I thought she was completely boring and now she's my favorite "representative" girl. she's generic, but she's generic in a charming and unique way, even though that contradicts itself lol