Joe intentionally pronounces various Japanese words wrong to annoy the weebs in his audience. Sometimes these phrases may also lead to the corruption of the English language.

This is a Joeism
When Joe says this, it's not a reference to any stream. It's just something he says sometimes.

"Tsundere", (ツンデレ, pronounced [t͡sɯndeɾe] [Soon-dare-ay]) is a Japanese word mainly used to describe a standoffish-but-warming character archetype in Japanese fiction, which Joe pronounces as "sun deer" instead.[1]

References
  1.     “Joseph Anderson Channel Two” video: “Undertale First Blind Full Playthrough” at 00:56:43.