How was I being a dick about a mental illness? What I was on about isn't a mental illness, I wasn't suggesting he was depressed or schizophrenic or OCD or something like that.
I was on about music, and the listening, appreciating and understanding of music is something that happens mentally, and it's obvious that they don't like it, so I made the joking assumption that liking Maiden was the norm, and given music is by it's very nature objective, it's the subjective interpretation that occurs mentally that is the difference between people liking and not liking it, so when coupled with my premise that liking maiden is the norm, there must be something not firing, or not quite right to not appreciate maiden.
It was basically logic and a tongue in cheek assumption.