1) A completely out-of-context shitty thing to do or say, especially from an unexpected source. From the elderly phrase "bolt out of the blue", but modified with skidmarks for flavor.
2) (driving) Some asshole coming from out of nowhere to bust your chops (cut you off, tailgate and honk, etc.)
1) Our night out was pretty bangin' until Chess Club Bill dropped that ear-splitting N-bomb at the bar. What a bolt out of the brown!
2) Jesus! Where did this pissed-off horn-addicted Excursion-driving dickhead getting all up my tailpipe materialize from? This fat bastard was a bolt out of the brown!