They sweat a while, but some of them take it real well, for a while. They take on the role of the subservient FO, which is just winding the douche-bag Captain spring inside. Beware of the FO that's sweating profusely with a weird nasty grin isntead of a smile.

I think doucheness is a personality trait, and so deeply engrained that a brief sentence as a FO won't cure the itch, just make them more agressive. Just look at some of the super-senior guys you might fly with. The real young guys that were quick upgrades can be either apreciative of their good fortune, or total entitled pricks that feel no pain but their own. Either way, their fast advancement becomes a personality mutliplier.

This is where the length of the mainline FO position becomes critical. You can only fight your own nature so long. I assume this is why we at Delta like to not upgrade right now. By the time you finally get there, you're a super nice guy (or you just snapped, or you dropped from a coronary event in your tenth year). At upgrade, I assume you're so worn out you don't even have the energy to be an [deleted] anymore.

Throw in a little furlough for character development... Say, I must be one hell of a nice guy!