It's just Shatner's peculiar delivery of the line that makes it sound like a slurred "Sir D'Amato".
If you listen closely, throughout the series you'll also hear him address "Miss Spock" and "Misser Sulu".
Not to mention in "The Gamesters of Triskelion" he shouts "What's happening to Lt. Youhura?!!"
Quite true. And we thought Nimoy was the drunk one!