Well, this is your chance to take the higher ground. Get some sweet headphones.
Maybe the guy has kids or something, I don't know, but the tunes seem to be really pissing him off. Yes, that's his problem *, but you could take pity, although maybe he'll just find something else to be angry about.
* well, it might be - the flats might be badly constructed or not fitted out right or old to the point where your tunes are being amplified around his place