All Time Low went guest-mad at the Anaheim, California stop of their Sad Summer Fest tour over the weekend. The Baltimore pop-punk kings were joined by Heather Baron-Gracie from Pale Waves, who came on for PMA, the recent single on which she and the band collaborated. But because doing two things is better than doing one thing, Demi Lovato also came on to sing Monsters, their duet with the band from last year’s Wake Up, Sunshine album. Check it out… ATL frontman Alex Gaskarth and Heather recently spoke to K! about teaming up for PMA. On how the song came together, Alex explained, “This whole thing kind of happened out of the blue.” “We’d never really linked up before, or met, apart from in passing,” he told us. “When we wrote PMA I felt like it would be cool as ...