As of r8362 & GameDir r2356, there is a new character trait, Coward:

Mercs with this trait

• Gain morale when they retreat (MORALE_RAN_AWAY_COWARD in Morale_Settings.ini)
• Lose morale when they encounter a numerically superior enemy force (when the enemy forces outnumber mercs + militia by a factor >= 2) (MORALE_ENEMYGROUP_COWARD in Morale_Settings.ini)

While reading through edmortimer's take on the characters, I noticed we could use this one (it is now used for Biff and Lance), but this was only in old character traits, not Sandro's revamp.
We could also recreate the Asshole character trait, but... it does exactly nothing in the old code. I'm not sure what to put there.

What exactly are the tactical/strategical benefits to being an Asshole? Help me out here, community!

What makes an asshole in JA2? Just a few ideas:

I guess he thinks very high of himself and would lose more morale on being injured because who the f... could hit the almighty asshole (tm)? On the other hand he would gain morale if others are injured, enemies of course, militia, even members of his own team.
He might not mind or even gain morale for civilian casualties.
He may get a bonus to the "Threaten" approach when talking to an NPC.
He'd probably be angry if other members of his team get better equipment, are treated before him when wounded or killing an enemy that the asshole already hit. "Hey, you took away my kill, dumbass!"
He might get penalties for certain assignments because he considers them beneath him.
Patients might have less heal rating if the doc is an asshole.
Other mercs might learn to dislike or hate the asshole and finally quit if you don't get rid of him.