Sure: if you're concerned about them, you think their action/attitude may pose a serious issue, and you're going to refer them to Pro Standards, you certainly ought to chat with them.

If you just think they're stupid, but not dangerous, I don't see the point of one Captain going to another to offer dual instruction on-the-spot.

I've seen it done before, and it was rather ...ironic.

A jumpseater, whom I had flown with earlier (hint: train wistles at push-back with "all-aboard" announcement, and guitar concerts in cruise), was deplaning. As he deplanes, he has a "picket-to-tittsburgh" moment. When he really should have said "thank you for the ride", he instead told my Captain that "his uniform was not regulation".

As luck would have it, this CRM genius wasn't simply rude, he was also absolutely wrong: my Captain's uniform was 100% legit. What made it more amusing still: my guy was a bonified troop leader, one that would have every merit badge, if only Delta awarded them. I thought he might have a coronary event, but to his credit he simply glanced up, nonplussed, and suggested a little FOM refresher to our Jetway CFI.