Christina Aguilera may have opted out of the fourth cycle of "The Voice,"
but that doesn't mean she won't miss her fellow coaches ... especially Adam Levine
. "When me and Adam are on breaks backstage, you know, we're writing profanity with my red lipstick all over Blake [Shelton]'s trailer while he's napping inside," she told E! News
. "It's like we have definitely become like brother and sister. We goof around and play around. I'm going to ...