Paris Hilton -- Hangs w/ Ultimate Lohan Enemy ... THE FIRECROTCH GUY

Paris Hilton has reawakened one of her strongest anti-Lohan alliances -- her friendship with Brandon Davis -- AKA the guy behind the legendary "Lindsay Lohan Is a Firecrotch" attack!!!

Paris and Brandon were spotted together at the Jay Z concert in L.A. last night ... and we're guessing the timing of the public reconnection is no coincidence, since Paris is back at war with Lindsay.

Of course, Davis (grandson of oil baron Marvin Davis) annihilated Lohan back in 2006 ... going on one of the most epic street rants of all time ... ripping her for her body odor, the color of her genitals ... and her financial situation.

Paris was by Brandon's side during the rant, cackling the entire time.