I'm not catholic so please help me out here. If you cannot use requested pronouns, does your religion also ban you from using nicknames? Is it okay for you to be called User23? Is it okay to say someone's cat is cute even if you don't really care for cats? What do you do if your partner asks if they look good or bad in something?
These are all reasonable questions. I'll answer as best as I can, but please understand that I'm not any kind of formal authority.
> If you cannot use requested pronouns, does your religion also ban you from using nicknames? Is it okay for you to be called User23?
I don't know of any Catholic doctrine that says people can't use pseudonyms, nicknames, or even change their name altogether.
> Is it okay to say someone's cat is cute even if you don't really care for cats? What do you do if your partner asks if they look good or bad in something?
Is it a lie, which is to say a falsehood told with the intent to deceive? Then yes it's wrong. Wouldn't you want to be told the truth if you in fact looked bad? Wouldn't you want to know that when you're told that you look good that you really do?
Personally, supposing I didn't think the cat was cute, I wouldn't say I thought it was. I would most likely treat it as a good opportunity to say nothing on the subject. Some theologians put forth a doctrine of "mental reservation"[1] which somehow makes lying OK, but I have to admit I'm not capable of the necessary mental gymnastics in any but the most clear cut cases.
Is it possible to say nothing about a trans co-workers transition then? If Jessica is now Kevin, what's the difference between that and Jacob going "nah call me Jake"? Is it just that you can't call Kevin he/him pronouns? Can you call Kevin as Kevin?
I'm unwilling by act or omission to knowingly indicate that I believe something that the Church teaches to be false. Thus, it depends on whether or not I'm being asked to participate in a deception, which I will not do. On the other hand, unlikely though it may be, if it's somehow clear that "Kevin" has no intent to deceive and is not deceiving anyone about her sex then I don't have an absolute moral objection to calling her that. This scenario is contrived and unrealistic, but it is largely a matter of prudence. Thus if I did surprisingly find myself in a similar circumstance, my actions would depend on the details.
As another Catholic commenter said, we owe Christian charity to all other human beings, including those affected by gender dysphoria. However, charity doesn't mean being "nice" or "accommodating," but it does require respecting the dignity of the human person. One way to respect that dignity is by not encouraging or condoning disordered behaviors or beliefs. I wouldn't offer a recovering alcoholic a drink, even if it was really great stuff.
That leads to another pragmatic matter. No matter what disordered beliefs or behaviors a person has (and I have my own share), we should want to help that person come to a rightly ordered place. There's really no one size fits all approach to that.
To your first point, pronouns and nicknames are not the same thing. Pronouns indicate that a man can become a woman or vise versa which is not what the Catechism teaches. Additionally, calling a cat cute if you don't care for them is lying which is a venial sin (meaning you probably won't be damned to Hell for it but one should confess if they sin regardless).
Catholics are called to Love (God is Love) and to love all sinners but hate the sins. We know that Church is a place for imperfect humans and thus we do seek to purify our souls with prayer, works of mercy and the Sacraments.
So with all the above in mind, we usually tend to avoid pronouns and refer to transgenders by their name instead. However, out of basic respect and good manners we can all call them what they want if they insist.
Jesus commands us that we must be known as his disciples by our love. Christian love begins with basic respect and good manners. Selfless love does not begin with requiring others to conform to our doctrine.
St. Paul said that he became all things for all people so that he may save some. We should do the same.
1 Peter 3:15-16 be ready to give an explanation to anyone who asks you for a reason for your hope, but do it with gentleness and reverence,
