He knows the exact date he impregnated her mother.
The presumed daddy says he bedded former Playboy Playmate Anna Nicole Smith on New Year's Eve 2006, a little more than one year ago.
Perhaps Birkhead should've protected himself a little better when he did because such gross actions - have you seen Anna Nicole Smith pictures? - have led to a bitter paternity battle with the reality TV star, who claims the baby's father is actually her lawyer and companion Howard K. Stern.
"I've always maintained from day one I was Dannielynn's father. My little baby was actually conceived last New Year's Eve," Larry said.
Sort of makes you more grateful for how you spent this December 31, doesn't it? Especially if you're Nick Lachey and Vanessa Minnillo.