Without a doubt, The Decemberists.
Can't call myself much of a Sufjan fan but I can appreciate a few songs in small doses and in the right mood. Other than that, the worst that would happen is that I would get bored and do something or fall asleep.
With The Decemberists, it's the opposite side of the coin. They make me want to kill or be killed as they irritate me that much! They are at the bottom of my barrel next to Erase Errata who put me in the same mood. My world would be a much happier place without either of these bands.
In all fairness to the band, it's mostly Colin Meloy's musical stylings, especially his vocals. I cringe whenever I hear that man sing. If I was ever to bitch slap anyone, it would be him. Just keep him away from me. Especially away from my ears!