Personally when I see bad behavior by other passengers and the FAs/GAs/check-in agents handle the situation well I write into UA with a compliment, especially when the passenger has threatened the UA staff with reporting them. A few years ago I tried to intervene and support the UA staff and got yelled at by the passenger including many profanities, so these days I quietly mention to the UA staff member to ensure they get my details from the manifest if they need a witness, and then follow up to UA with my details of the incident in support of the staff member. By doing it soon after the incident is fresh in my memory and the details still front of mind.
Kudos to the FA, pilot and GA for handling it as well as they could under the circumstances.