When you find that sweet spot between funny and serious... A character that is a single really bad joke but fleshed out so much that people don't realise the joke until several sessions in... Ooh, that's the good stuff.
I once spent an inordinate amount of time fleshing out a character who was low-key meant to be the dwarf equivalent of Indiana Jones. Used a chain whip, had a trademark hat and the first name of a well-known dwarven realm, was trained in history, etc.
In our first session, I rolled a crit fail on an athletics check and fell into a chasm full of magma. It was the equivalent of Indy getting smashed by the boulder because he tripped. I didn't even get to pull out my character's irrational fear of drakes.