Katherine Jackson -- PISSED That Jermaine Bought Ferrari

Katherine Jackson feels like SHE'S been taken for a ride ... by her debt-plagued son Jermaine, who plunked down a huge amount of cash on a Ferrari ... sources close to the Jacksons tell TMZ.

As we reported ... Jermaine spent more than $160,000 on a Ferrari smack in the middle of jury deliberations in the Michael Jackson wrongful death trial -- perhaps banking on the fact that his mom would come into a boatload of cash.

We're told Katherine is livid because she has recently bailed him out of debt. We're told Jermaine's baby mama Alejandra came to him for rent but he didn't have the cash, so Katherine anted up. She feels it's totally irresponsible of Jermaine to spend $70,000 for the car (he got around $90k for the Rolls he traded in) when he can't pay his bills or his child support.

What's more ... we're told Katherine is griping that she was talked into filing the wrongful death lawsuit by Jermaine and Randy, and she's experiencing a pretty severe case of buyer's remorse.