To unlock the Extreme Personality trophy in Red Dead Redemption 2, you must reach the maximum or minimum honor level in the game.
Honor in Red Dead Redemption 2 is a system that isn't immediately obvious but it is important. It will track how you act throughout your time with the game and will determine how other characters in the game interact with you and if you receive discounts from stores.
The Honor scale in Red Dead Redemption goes from -8 through to 8 with 0 being neutral.
Taken from the Red Dead Redemption 2 Guide:
1. This can be achieved after [Paradise Mercifully Departed] in Chapter 5
2. Chapter 6 will have 1.5x multiplier, so it will be easier to get in Chapter 6, but NOT must.
Here is a list of the actions that affect your honor:
Increase Honor in Red Dead Redemption 2:
Donate cash or jewellery to the camp tithing box
Disarm an opponent during a duel rather than killing them
Peacefully surrender to the law and do your time in jail
Complete chores around the gang's camp
Kill rats in town
Pay off debt at post offices to clear your bounties
Decrease Honor in Red Dead Redemption 2:
Watch an animal bleed to death
Scare civilians by shooting near them
Steal a horse hitched to a post
Knock out a civilian and loot them
Trample an innocent civilian with your horse
Intimidate or beat someone in a robbery
Kill domesticated animals (dogs, pigs cows etc)
Shoot or use explosives on specific graves or dead bodies
Hold up a store and steal from the cash register
Antagonise or intimidate someone
Watch your horse writhing in agony without helping it
Kill an animal and leave without skinning/stowing it on your horse
Kill a civilian or lawman