About person-first language
Person-first language has different connotations for different groups. Some groups prefer it; others find it offensive. It’s not inherently good or bad, in itself, but it’s taken on strong associations because of ways it’s been used.
The most important thing is what you mean, and people should make an effort to understand what people actually mean rather than focusing primarily on the words they’re using to say it.
That said, it’s harder for people to know what you mean if you use language that is normally used primarily by people who don’t respect them.
With that in mind, here’s what I think I know about person-first language:
Saying “a person with a disability” is usually not regarded as offensive. Saying “a disabled person” is sometimes regarded as offensive, but it’s not as likely to cause offense as some other things. Sometimes people shorten this to PWD. That’s not rude, but it might not be understood.
Many autistic self-advocates are offended by “person with autism”. Many parent-centered organizations are offended by “autistic person”. Telling an autistic person that they should be using person-first language is *extremely* offensive, because it’s suggesting that you are either only aware of the perspective of parent groups or that you think the views of parent groups are more important than the views of autistic people.
Calling a deaf person a “person with deafness” or a “person with a hearing impairment” is likely to be regarded as extremely offensive – especially if the person you’re referring to identifies as Deaf. (I don’t know how to explain the difference; I very much hope someone reading this does.)
“Retarded” and “Person with mental retardation” are both offensive, because they have an extensive history of being used to dehumanize people. Using person-first language doesn’t fix that. “Retard” is *extremely* offensive, because it’s almost *always* used in dehumanizing ways.
People with certain types of mobility disabilities often prefer person-first language, but I don’t know enough about this to explain it.
For sexual orientation, hardly anyone uses person-first language, but it doesn’t have as strong a connotation. It’s not offensive to call someone gay, or a gay person. It’d be a bit weird to call someone a person with gayness, and a bit rude to say “a person who happens to be gay” or “a person who is gay”, but it’s not really the same kind of thing exactly.
For race it’s more complicated than I know how to explain but: using noun forms is almost always considered rude. (Eg: don’t call people “blacks” or “whites”). Using person-first language is *sometimes* ok, and sometimes likely to be offensive, and I’m not sure how to explain which is which, except that you shouldn’t say “person with *ness” as a way of referring to race.