In one of three Nevermind songs to feature guns prominently in the lyrics, Cobain painted a thumbnail sketch of a character whose life consists of bad parenting and blissfully stupid rock n' roll escapism.
The character lives for the moments when he's swept away by a "pretty song" to which he'll sing-along. Maybe he'll even get happy enough to fire his guns. The happiness isn't too deep through - the guy has no conception of what he's singing along to, and no self-awareness. In biblical syntax, he knows not what it means.
At the time Cobain wrote 'In Bloom', the kind of dumb rock fans he had in mind were still a bit of an oddity at Nirvana shows.
The beauty of 'In Bloom' was that while it was a sly and satisfying condemnation of this kind of fandom, it was also an exciting enough rock tune zo engender mass sing-alongs. It managed to satisfy egghead ironists and blithe moshers with the same chorus.