In the movie The Dark Knight, after Joker captures Lao from the Jail and brings him back, he gets his share of money. Then he burns it? Why did he burn the money? If you say Joker is a Psychopath and "he just want to see it burn", that can be accepted. Joker is a Psychopath, but the people working for him are not right? Why would they allow Joker to burn so much money. They would just hit him and run with the money.
From the Wiki (of course we all know Wiki's can be wrong, but we'll assume they're close to the truth):
The Joker's Thugs were a gang of criminals, in part a combination of small-time robbers, bounty hunters, shanghaied gangsters, and mentally-ill escapees of Arkham Asylum, who served under the Joker. Because of the Joker's appearance, most of the thugs wore clown masks and similar apparel.
Now, that same page also lays out the scene in question:
Ending the Chechen's Regime
The Chechen met the Joker on a Container Ship with his thugs and rottweilers. The Joker burned his half of an immense mound of US dollars, which happened to be holding the mobsters' half on top of it, and betrayed the Chechen by having his own men join him, and possibly execute their former boss; also possibly involving cutting him up into tiny pieces and feeding them to his beloved rottweilers. There are only four thugs.
IIRC, it's accurate to say there were only 4 thugs present. So, Joker most likely picked 4 mentally ill, least money-driven guys to accompany him on that job. They want Anarchy, not money. Maybe they were pyro's. Maybe they were mass murderers. Who knows. But Joker would have selected them because they'd be least likely to want what he was about to burn.
His extreme flamboyance "sending his [typical] message".
The Joker was another extreme character in Gotham where everything is already exaggerated especially the Batman.
The Joker doesn't just rob a bank, he robs it and serially kills his accomplices and leaves them at the scene.
The Joker sends death threats pinned to the chest of two corpses whose last names equal the threatened (Harvey Dent).
Killing a money laundering rat like Lao by burning him with the very same money he helped crime lords abscond with is the minimum required atrocity by an extreme villain with a violent reputation.