Iggy Azalea Describes Lighting All of Nick Young's Designer Clothes on Fire

Hell hath no fury like Iggy Azalea scorned -- just ask Nick Young, who had all his designer clothes LIT ON FIRE by his ex-fiancee ... after he got caught with his pants down.

"I burnt it all ... and I threw stuff in the pool, too," Iggy said, smiling.

Remember -- the rap star and NBA baller had a pretty messy breakup back in the day. We already knew Iggy dumped a bunch of Nick's crap on her driveway and personally got his car towed.

And now, we got the play-by-play of Iggy going full pyromaniac on Swaggy P's entire closet!

"I texted him a video and I’m like, 'Hey, I’m burning your s**t ... I don’t know where you’re at, probably with some girl, so I hope you get home quickly because I’m moving on,'" Azalea told Andy Cohen on 'Watch What Happens Live.'

To be fair, she also warned him -- "We're progressing on the spectrum from cheap to expensive."