(Image Credit: Townsville Coroners Court/AP Photo)

Why would a grieving man send friends a Christmas card with a wedding picture of his dead wife and a reference to his own good looks?

Gabe Watson, in an exclusive interview with "20/20? co-anchor Elizabeth Vargas, addressed what some have criticized as inappropriate behavior following his wife's drowning death, including mailing that eyebrow-raising holiday card.

He called the card "an attempt at humor."

Last week, an Alabama judge dismissed a murder charge against Watson, whose wife Tina Watson died on a scuba diving trip during the couple's 2003 Australia honeymoon. Nicknamed the "honeymoon killer," Gabe Watson served 18 months in an Australian jail after pleading guilty to a negligent manslaughter charge for failing to save his wife of 11 days. But at his U.S. murder trial earlier this month, the judge ruled there wasn't enough evidence to convict him.

Watson has insisted that he never intentionally harmed Tina, but has faced a barrage of criticism over how he acted after Tina Watson's death. Friends said they were disturbed when, during a gathering following Tina Watson's 2003 funeral, Gabe Watson showed honeymoon photos of Tina Watson standing next to signs warning of drowning danger.

"That was like almost foreshadowing something tragic that was gonna happen," said Tina Watson's friend Melinda Kayton.

Two months later, Kayton said she received Gabe Watson's Christmas card, which she said featured a wedding picture of Gabe and Tina Watson, along with the message: "Who's that good-looking guy standing next to Tina in the picture?"

"That's just tacky," Kayton said.

But Gabe Watson told Elizabeth Vargas that the card - which was sent to dozens of people - was simply referencing an inside joke from the wedding. Before the wedding ceremony, Watson said, one of Tina Watson's friends asked "Who's this good-looking guy?"

"I'm kind of looking around. I go, 'Oh, that's me,'" Gabe Watson remembered.

"It was an attempt at humor from an inside joke," he said. "I thought, well, all these people have tried to remind me of funny things and make me laugh that I thought, well, maybe (the friend will) remember it.  And maybe it'll make her smile."

Watson said that the warning sign photos were also intended to be humorous in nature. Watson, who has since remarried, said he and Tina shared a "warped" sense of humor.