Silky
You miss the point completely - it's not that we don't dislike the "thumb print screens" - none of us want that, but it's none of my business if he/she chooses to do it.
It's the debrief "in no uncertain terms" from one professional to another on a completely irrelevant issue. If you want clean screens, clean them.
Should we as Captains debrief our FOs in "no uncertain terms" every time we see something that we don't like? ...because it's one of our beefs...?? Well the FO on that flight will now see that it's acceptable for a senior trainer to admonish a TRI for pet peeves and said FO may take it upon himself to do same when he goes left...as we've all seen.
f.