A speaker cranks up his truck stereo until the bass makes the mirrors flex and the whole vehicle shake, but the noise can't drown out what he's really feeling. He's heartbroken over a girl who has moved on to someone else. The poem traces his pain in three steps: it began when he saw her, got worse when she kissed another guy, and eased when he realized she didn't miss that guy either.
What makes it feel honest is the gap between what he says and what he feels. He claims he's moved on, then adds "or at least that's what I say," which gives the game away. He takes some comfort in believing she still thinks of him, and he admits he wishes he had what they had. The closing line, about finding "a new fiddle to play," tries to sound defiant and casual. The mood is restless and wounded, with a bit of swagger covering the hurt.