Figure the title is pretty self-explanatory. But if need be, if I were to mention I'm getting a large refund this year, or getting audited, or anything in between, am I walking on thin ice talking about this?
You didn't mention the country... In most countries, the company pays you a salary, and deducts some amount of tax off the salary, sending that money to the tax office. This should more or less reflect what taxes you owe, but will always be a bit inaccurate. And at the end of the year, you fill out your tax return, where the tax office calculates exactly what you owe, and then you pay the difference or get a return. That is absolutely normal.
So a large tax return doesn't actually mean you get money. It means the company sent too much money to the tax office through the year, and the difference gets returned to you. It doesn't affect your financial circumstances (it may affect what you thought were your circumstances), so it is not really business related or sensitive information. It's personal, there is no need to discuss it at work, but there is no particular reason not to discuss it. It's like nobody can force you to discuss how your children are doing at school, but if you like talking about it in your lunch break, few people will be stopping you.
If you regularly get huge tax returns, then the company isn't calculating your taxes right, and you might complain to their payroll. (At one place, what I paid through the year was always correct within less than £3). This should never happen at a big company; at a small company where they don't have anyone doing payroll full time it might happen.
In general it is not a good idea to be sharing personal information. In particular I'd advise against sharing financial information unless there is a good reason behind it such as asking an expert for advice.
Work friendships can be fairly shallow (as can non work ones). You never know when something you said can come back to bite you. I would never let anyone know if I'm soon to get a windfall of money, some places it may be OK, but here it would be asking for trouble with people begging loans or worse.
I agree with gnasher729. Furthermore, you can if you're talking to payroll/HR/management (if they're the ones you negotiated your salary with) and it is a tax issue. Otherwise, if your just bragging about how you managed to deduct a large amount by maxing out an IRA or something like that, you're best off keeping it to yourself. And if it's a matter of you needing tax info, again, if it isn't payroll/HR/management (if they're the ones you negotiated your salary with) then don't talk about it.
It really depends on your specific office. Generally, your financial situations are your personal business and therefore nobody else really needs to know about them. However, if someone asks about them and you are comfortable talking to them about it, go right ahead.
If your work-environment is something like a large company and is more of a corporate setting, I wouldn't. However, if you work in a small startup where everyone is just pals, go right ahead. Again, it greatly depends on where you work and who you're working with.
You should avoid any specific talk. The underlying issue is that your tax refund gives others an idea of your salary, and that can cause resentment. It doesn't give specific information, but it gives people a rough idea.
I have heard people complain about due dates, and administrative nightmares caused by ridiculously low amounts (e.g., a colleague who spent many hours over a discrepancy less than $5), but being more specific is asking for trouble.