A while ago, I was asked to coordinate measures needed to complete a task. The task was set up to support an important customer C. One sub-task would have fallen to coworker X, who was the only one familiar with the technology involved.
To my surprise, when I asked him to solve the problems associated with his sub-task he responded with a reply like "Oh well, I don't like C, they're all stupid, I'm not going to do anything for them". In other words, he refused outright to do his job. I tried to persuade him to still look into his sub-task (I'm not familiar with the details at all), but always earned excuses and distractions from X. Needless to say, we didn't support C very well.
Being X's peer and not their superior, there wasn't much I could have done towards him. Maybe I should have reported his behaviour to my superior immediately.
Because of this and other similar issues, I'm trying to move inside the company. This issue is likely to come up in a meeting with my new boss, and I'd like to shed some light on what happened at the time.
On a scale from "Don't even mention it" to "Quote X word by word", what is the right level to talk about this dark spot?