Because there's a quote for every occasion1:
The question of how long someone believed in Santa Claus is a worthless topic that should never come up in conversation. Having said that, if you're going to ask me how much of my childhood I spent believing in an old man in a red suit, I can confidently say that I never believed in him to begin with.
I knew that the Santa at the preschool Christmas pageant was just a fake. Digging into my memories, I'm pretty sure that the other kids watching our principal dressed up as Santa didn't think he was real, either.
I was a precocious child who didn't need to see mommy kissing Santa Claus to question the existence of an old man who only worked on Christmas...
The passage then goes on to discuss such things as the non-existence of aliens, time travelers, and people with psychic powers, and how they don't exist, either. Really, the dumb bitch needs to quit contemplating his navel and answer his damned phone.
Oh, but St. Nicholas of Myra, patron of children, sailors, merchants, archers, thieves, students, and prostitutes2 (not to mention a host of places that have adopted him)? Yeah, that guy was real. And his feast day is December 6, not December 25.
1. For those of you that aren't snorting various kinds of mind-bending anime off of some moeblob's ass like it's the finest Columbian blow, that's the opening monologue from The Melancholy of Haruhi Suzumiya. This translation is actually from the North American edition of the novel, done by Chris Pai.
2. Actually, the tradition of anonymous gift giving on his feast day, a custom later moved to Christmas during the Protestant Reformation, developed from the story behind the last one. Wikipedia has an abbreviated version here. It's the last two paragraphs.