Katy Perry's feud with Taylor Swift seems like it's from a different era of celebrity entirely. Whether it started because of John Mayer or because Perry stole some backup dancers, it's pretty clear that it's been on like Donkey Kong for quite some time. There's been the scent shade, the Kanye concert shade, and the song "Bad Blood." If you didn't know, Swift's hit is allegedly a hit on Perry. Now, Perry has responded with a little subtle shade of her own. She retweeted a fan wearing a "Bad Blood" shirt while posing next to a Perry disco ball. The tweet is so shady that the shirt's logo is even in the shade. Now that's what we call shade. Jezebel's Bobby Finger first noticed the t-shirt, which most would miss. But not the shade-sleuths of online. We catch everything. Here's the tweet.