8:02 AM PT -- Diddy's attorney Marc Agnifilo tells TMZ ... "This man [Cardello-Smith] is a convicted felon and sexual predator, who has been sentenced on 14 counts of sexual assault and kidnapping over the last 26 years. His resume now includes committing a fraud on the court from prison, as Mr. Combs has never heard of him let alone been served with any lawsuit. Mr. Combs looks forward to having this judgment swiftly dismissed."

Diddy just took a HUGE L in a sexual assault lawsuit he blew off, because a judge just slapped him with a $100 MILLION default judgment.

Derrick Lee Cardello-Smith, currently an inmate, claimed in his lawsuit Diddy drugged and sexually assaulted him at a party in Detroit back in 1997. It's unclear if the statute of limitations has run, but that wasn't addressed by the judge.

According to the lawsuit, the 2 were drinking and smoking weed at the party and got naked with a bunch of women. Cardello-Smith says he was performing oral sex on a woman when he felt a male hand on his left buttock -- he says it was Diddy's hand. A short time later, he says Diddy offered him a drink, which was spiked and he passed out.

Hours later, Cardello-Smith claims he woke up and saw Diddy having sex with a woman, and Diddy allegedly said to him, "I did this to you too."

Cardello-Smith sued for $100 million, but according to legal docs, it appears Diddy did not file an answer to the complaint. A hearing for a default judgment was set for Monday, but no sign of Diddy. So, the judge gave Cardello-Smith what he wanted -- $100 million.

The judge also set out a payment schedule -- installment payments of $10 million per month, starting October 1.

We've reached out to Diddy's team ... so far, no word back.