Adrien Broner has some career advice for Conor McGregor -- don't EVER try boxing again!

We got AB at 1 OAK in L.A. ... and the superstar boxer didn't mince words when it came to the idea of Conor hoppin' back into the ring.

"If he want this work, I’ma f**k him up," Broner told TMZ Sports. "But other than that, I want him to stay away from this sh*t."

Adrien says McGregor should go back to where he belongs -- the UFC -- cause a young hitter like him would do way more damage than Floyd Mayweather.

The former 4-weight champ wasn't done there ... telling us boxers could conquer MMA better than Conor did boxing, "cause we fight better than them." 

AB did have one other idea for the Irishman -- just call it quits!!  

After banking $100 MIL ... why not party forever?

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