"Good morning everyone, would anybody be available to answer a question? I am running into [describe your problem]. Thank you.".
Easy, polite and to the point.
Though we also usually have private team channels and separate support channels for a team in our Slack. I.e. the SRE team might have their own sre-priv channel for team chatter, and an sre-support channel for external support requests, so perhaps that is a function of this format.
You'll often see a new msg in the support chan with something like the following:
> Hey #TEAM, we're seeing an issue with the spline reticulator not reticulating splines. Started last night. Details in :thread:. Thanks!
followed by notes/logs/stack traces as needed. Works quite well, and doesn't choke the channel with endless walls of text.
I probably agree on the second, but I think the first is subject to what the definition of 'better' is. If someone has to give me, say, a bad evaluation of my performance, then the most efficient way for them to do it is to walk up, say "terrible performance" (and possibly list reasons), and leave—but I certainly don't feel, as the recipient of the news, that that is the best way for it to be delivered.
So if we're going to talk about communication efficiency, we need to define what's the goal being optimized here.
If a manager wants to minimize the time spent dealing with one of the engineers and wants to see this engineer quit, then the "cursory explanation" can be considered "efficient".
If this same manager, instead, wants to maximizes the odds the engineer stays and improves her/his weak points, then the "comprehensive" explanation might be a lot more efficient, despite requiring the manager to spend more time at it.
At work, efficiency is polite and predictability is nice.
Watercooler talk excepted, of course, and my company has a couple "watercooler" Slack channels.