Hmm.
This is stupid.
Ninjas don't write in diaries. Ninjas are awesomeness, throw shruiken, kick ass, and steal Cloud's materia, but they do NOT write in diaries given to them by big-bosomed bartenders for Christmas.
Heck, ninjas don't even celebrate Christmas, they just steal the gifts.
Hey, maybe Santa was a ninja. That's how he climbs down chimneys! And it'd kinda explain why he steals cookies, too-

"He doesn't steal them."
Hang on, someone's saying something- SPIKEY???

"…?"
"You MADE A COMPLETE SENTENCE that had NOTHING TO DO WITH BATTLE PLANS. Wow, I'm proud of you- HEY!"
"What?"
"YOU WERE READING OVER MY SHOULDER, YOU BASTARD, THAT'S MY PRIVATE DIARY!"
"No it isn't."
"Huh?"
"Ninjas don't write in diaries."
"And?"
"You're writing in something."
"…?"
"Since you're a ninja, it can't be a diary."
"Wow, you have got a brain under all that hair gel."

Later

Wow. Spikey had, like, LOGIC. And he didn't even have to ask Vinnie for help.
UNLESS HE DID. MAYBE HE'S TELEPATHIC! I knew that psycho Vinnie was a vamp.

"You'd use up less space if you didn't write in uppercase."
"ARGH! AGAIN? YOU ARE TELEPATHIC; YOU KNOW WHEN I'M WRITING, DON'T YOU?!?"
Oh, my GAWD. Did he just smirk? It was there, I swear. It was friggin' tiny, but it was there.
…This isn't right. He's supposed to have the IQ of Tifa's wilting HOUSEPLANT.

"140."
"You're still here!?!"
"No."
HE DID IT AGAIN. THE BASTARD IS SPYING ON ME. I'M SWITCHING ROOMS.