I think its referencing to one of Kiara's sims stream where her sister sent her a graph of what she think of the holoEN and Kiara was below bottom left being dumb and horny
It's referring to a chart measuring intelligence at the top, idiocy at the bottom, lewdness on the left, and pureness on the right. It was during a HoloEN collab stream iirc. When Kiara's name came up, her artist immediately yelled in the chat "BOTTOM LEFT". It has of course become a recurring meme. It's long since stopped being limited to Kiara, as well. Everyone is Bottom(Dumb) Left(Lewd).