File this under: "The Problems of VERY Rich People."
Kevin Costner has been dragged into a nasty legal war with his neighbor in Carpinteria, CA -- an upscale beach community near Santa Barbara.
Long story short -- the neighbor, Rick Grimm, claims he bought a SICK beach property back in 2009 with KILLER views of the ocean and coastline ... and it happens to be located right behind Costner's pad.
Problem is ... the neighbor claims Costner is paranoid about his privacy and planted a bunch of trees and shrubs to make sure nobody from Grimm's property can see into his home ... trees which are now blocking Grimm's once-spectacular view.
Grimm filed a lawsuit, obtained by SBView.com, claiming he TRIED to play nice -- sending multiple requests to Kevin and his wife to trim the hedges -- but the Costners blew him off ... and planted even TALLER trees.
Grimm says Costner is contractually bound to NOT plant trees which obstruct Grimm's view ... but Kevin doesn't care. According to the suit, Kevin made it clear to Rick's people he would not "back down" and would "do everything in his power to secure his privacy."
Grimm is now asking a judge to force Kevin to chop down his trees ... PLUS he wants at least $150,000 in damages for loss of enjoyment and $500k for damage to his property value if the trees don't come down.
A rep for Costner had no comment.