First the Deshon Marman debacle, now this. Looks as though another chapter just unfolded in airline saggy pants saga, and this time it involves a bigger local celebrity: According to a new gossip report from the Merc, Green Day frontman Billie Joe Armstrong was kicked off a Southwest flight from Oakland to Burbank for letting his pants hang too low. Armstrong griped about it in a tweet published Thursday night. In contrast to Marman, though, he wasn’t arrested, and probably won’t incite any protests. But he may write a song about it.