Christina Aguilera is one of Brainulator9's most recent waifus since around July 2015.
Cavia porcellus noted the abundance of Xtina puns related to a video-game character named X-shot (sometimes referred to as "Rotobaga"), especially after its release. Cavia thought that these puns were innocent as he thought that Aguilera didn't fit his idea of Brainulator's random-but-not-that-random personality. However, he was later proven wrong.
Brainulator9 has recently used Aguilera for one of his avatars on Wikia.