Conrad Murray : Delightly Lunch With MJ's Former In-Law

Michael Jackson's family must be going ballistic over this ... Conrad Murray had a delightful lunch with Janet Jackson's ex-husband Friday.

The man who killed Michael dined at Crustacean in Bev Hills ... with the guy who was once his neighbor. You see, James DeBarge was jailed in 2011 after being busted on drug and weapons offenses. Michael's former brother-in-law and

Murray were in the same cell block at L.A. County Jail.

The chick is Nicole Alvarez ... Murray's most recent baby mama.