Etymologically, it's an interesting history.
Dormies have rarely been seen, but they are thought to be a rare subspecies of the wombat family native to the Scottish Highlands.
In one of nature's crueler evolutionary tactics, the Dormie's defense against predators is to have a nearly fatal heart attack and to emit a putrescent smell from its "death glands" located in its anus, (this is because its natural predators, birdies and eagles come from behind).
The only known sighting of a wild dormie occurred In 1620 during a match between Liam MacBarelegs and David MacLegsarebare.
On the 17th at St. Andrews, Liam, who was leading the match by 2 holes, but had driven into the left side fescue, flushed out the dormie while looking for his ball.
The dormie flew out of the fescue with a start (they can only fly short distances from the fescue) and across the fairway.
David, who was in the middle of his swing when all this happened, hit a monster slice that surely would have been the end of the match, if a wandering eagle hadn't spotted the dormie out in the open.
As the eagle flew in from behind to attack the dormie, MacLegsarebare's errant approach shot coincided squarely with the eagle's jutting talons.
With a golf ball now impaled on the now freaked out eagle's little toe, he tried to fly off toward his aerie, but the off-center weight and wind resistance created by his new adornment caused him to fly in a slow right to left arc directly over the 17th green.
As the eagle finally shook the ball free from his bruised toe, the ball fell with a soft plop 2' above the hole, caught the slope, then slowly rolled into the hole.
MacBarelegs was so disheartened by the events that he couldn't regain his composure at the 18th. He drove into the road, where he broke the windshield of a 17th century Saab, cursed, and walked off the course in a huff whith the match all square.
Ever since then, "Dormie" has been used when a player needs only to halve a hole to win a match. It's not an announcement so much as a warning, shortened from "gg, but watch out for a f&*%ing dormie"
Hope this helps