A disorder is a disorder. I don't see anything wrong with referring to a disorder as such. For instance, there are people with conditions that are considered mental disorders, so saying they have a mental disorder while talking about them isn't necessarily an insult.
What makes calling homosexuality (or whatever it is that they're talking about earlier in this thread) a mental disorder an issue here is, it's not generally accepted as such. Whether homosexuality is a disorder or not is a different story altogether, but if saying something offends a lot of people in a negative way, then it's probably better to avoid saying it.