system
Given the following post, respond as if you're commenting on Reddit:
human
[Batman TAS] What makes Joker so afraid of the IRS and jail?

He was trying to clean his name in that episode (Joker's Millions), but surely someone of his caliber shouldn't be afraid to go to jail if something goes legally awry.  Does he prefer to be put in straight jacket than to be given free rectal exam in the showers?

Maybe that was merely warn kids about the real life "villain" that is the IRS, but I was asking about the in-universe reason.
gpt
Given the Joker's habit of "committing to the bit", there is a chance this is him doing a "meta joke"; Joker will poison Gotham's water supply, shoot a police chief's daughter and try to brainwash Robin, and go toe-to-toe with Batman nightly. But deal with the IRS?!? No Thank you! 

In reality the Joker doesn't give a crap about taxes, buy it promotes his image of being crazy and chaotic.