All the classes' normal personalities are subverted, so, for example:
The bard is the rational, responsible one who always keeps it in their pants
The ranger is super social and loves people, is very charismatic and not at all weird
The rogue is super generous and sleeps at normal hours. They also never break off from the party to commit shenanigans
The barbarian is learned and articulate. They don't actually like fighting all that much, though they recognize the need for it
The cleric is like a frat bro. They only joined their order because their best friend was joining, they like to fight and hate spellcasting. Also, they don't take religion seriously
The paladin is the cleric's best friend who actually prefers spellcasting and retroactively wishes they had become a wizard. They're not super religious either
The druid is not in tune with nature AT ALL. They grew up in the suburbs and have only seen a tree like, thrice
The warlock is super peppy and loves bright colors, much to the chagrin of their dark, eldritch-horror patron
The sorcerer understands their magic perfectly and chooses to use it only when necessary. They're not that good at talking to people and prefer to read books instead
The fighter, despite knowing how to use every weapon under the sun, chooses to stick with their trusty daggers, even when there's a legendary sword three feet away. They are calm and strategic and never rush into a fight.
The monk grew up in a large, loving family who they still visit often. They are easily scared, lack common sense, and will never start a fight. Or an arm wrestling match
The wizard looks dignified and is ACTUALLY dignified