See, that's why I think there's more to it. It's earnest and ironic at the same time. He joined the DEs with doubts from the beginning. I was trying to work out the timeline the other day and he wasn't a DE for very long - he was trying to get a job back at Hogwarts in less that two years after graduating I think.

Either that or he just plain hates himself - and taunts himself with his tainted blood.