Is it okay for a reviewer to share an under review manuscript with their colleagues? In a research meeting I mentioned I was doing some peer-review for a conference and disclosed the general topic it was about, without any further details. Immediately my colleagues demanded I disclose information about details of the paper, authors, and they even suggested I should share the paper with them immediately, and they swore "they would not share it with anyone".

I refused and said this was unethical behavior. They all got really angry and took it personally, saying that sharing a manuscript under review was completely normal and ethical, and even recommended and the problem was simply that I did not "trust them".

What is your experience with this? What are your thoughts?
Do not share this manuscript.

It is one thing for you to solicit input, under an agreement of confidentiality, when you recognize there is another expert who can help with the review.

It is totally different when someone demands that you share it, not because you are getting help with the review, but for their own edification.  The manuscript is confidential.  Keep it that way!