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.