The '30 Rock' star - who allegedly "pushed and shoved" snapper Marcus Santos in New York on Tuesday morning - broke the tension on the US talk show by taking to the stage to Pat Benatar's 'Hit Me With Your Best Shot' and he then announcing he had lost weight before pulling down his clothing as proof.
He then jokingly urged host David Letterman to show a picture of yesterday's New York Daily News newspaper front page, which features the headline "30 Rocky" and a large picture of Alec appearing to strike the paparazzo.
David dangled the newspaper in front of Alec's face before saying, "The picture, without knowing the story, tells a tale that's not often true."
Pointing a finger at his image, Alec replied: "I'm forming the letter 'F' with my mouth, and what I'm saying is, 'What the F - stop are you on with the camera?' "
Alec is alleged to have been involved in an altercation with Marcus - who works with the New York Daily News - when he was leaving the New York City Marriage License Bureau with fiancee Hilaria Thomas, where he is said to have grabbed another photographer.
The 54-year-old star has also been accused of rolling his mountain bike over a TV reporter's foot outside his East Village apartment following the first incident and he is then said to have used his handlebars to knock the Inside Edition journalist aside when she questioned him about his altercation with Marcus.
The journalist is quoted as saying: "Ouch, my back. He shoved me and ran over my foot."
But Alec maintains he is a victim in the whole episode with Marcus, telling the 'Charlie Rose Show': "The guy lunged and almost hit me in the teeth with the lens of the camera.
"So I just pushed the guy away."
But Marcus insists Alec punched him, explaining: "He comes after me, starts shoving and punching me - one time, right in the chin."