After music producer Calvin Harris and Swift called it off, their post-breakup feud centered around songwriting, but not in the usual revenge-hit-song way. While they were together, the couple collaborated on the Rhianna track, "This is What you Came for." However, per T. Swift's request, she was listed under the pseudonym "Nils Sjoberg." Going along with the story, Calvin maintained that he and Taylor hadn't collaborated musically.
But, of course, after the couple broke up, Taylor's people swooped in and confirmed whisperings that Swift had in fact helped Harris write the track. Harris, taken aback by the change in plans, went to twitter to say, "Hurtful to me at this point that her and her team would go so far out of their way to try and make ME look bad at this stage though." He later back-tracked and tweeted more amicable tweets about his ex, but good for him for publicly calling her out on her schemey bullshit.