Jermaine Dupri Says Yung Joc Reneged On So So Def to Join Diddy's Bad Boy

Jermaine Dupri is admitting he dropped the ball getting Yung Joc's 2006 No. 1 smash hit "It's Goin Down" for his So So Def empire ... all because he decided to go to bed!!!

The platinum producer revealed he had signed the song's producer Nitti to his label, and was expecting Joc to follow suit once he heard the song ... but the very next day the pair went over to Diddy's Bad Boy.

As they say, the rest is history ... the song topped the Billboard Hot R&B/Hip-Hop Songs for 8 weeks straight.

JD's "For Motivational Use Only" collaborator Curren$y quipped on "The Breakfast Club" ... JD should've "stayed up" -- which the platinum producer agreed, but also said he didn't actually sign Joc to lock him and the 3x platinum track.

The first version of "It's Goin Down" kicked off with the So So Def audio tag so JD thought the song was in the bag ... a costly mistake as far as Joc was concerned.

The Atlanta rapper recently ranked Diddy over JD in terms of marketing savvy on an episode of "My Expert Opinion" ... and also felt JD stretched his focus too thin for his liking.

JD still has the opp to get revenge against Diddy in their still pending Verzuz battle, which he insists is still happening -- but the 2 superproducers are plotting a bigger event than what fans are used to seeing.