His wife ran off with a Vulcan neuropressure masseuse.
Hence his bigoted, borderline racist attitude to anyone of that race.
Cut Spock some slack before you call him a green blooded person of questionable parentage. Geeze, the guy just lost his mother and most of people... Old (De) Bones' outbursts were often little more than frustrated replies to losing an argument. Generally funny too. Never kicking the Vulcan when he's down either.
He couldn't help, he was just repeating a line from the TV show. He knew he had to do that so people could say: oh, he soo nailed McCoy.