Some tour pairings make us scratch our heads wondering what (or if) the artists possibly talk about on the road. Charli XCX and Jack Antonoff are decidedly not those co-headliners. Hanging in the wooded lounge at the Sweetlife Festival, the Bleachers frontman and pop diva dished some serious sarcasm, finished each other’s sentences and shared what they’ve recently learned about each other as they prepare for the Charli and Jack Do America romp, opening July 21 in San Diego.     “He likes to