Because it had to be done. Well, more because I'm bored, really.
4.CiN - Time Crush
After leaving Martha on Earth, the Doctor is still desperately trying to decipher her mysterious codewords - "I'm obsessively in love with and want to do you in the dirt" As he continues to ponder these words, the TARDIS starts veering madly out of control. The Doctor moves to reset the controls-
and feels his arse being pinched. He turns around, and finds himself face-to-face with a fat, bespectacled old man in a nightmarish fluro multicoloured coat.
"Do you work out?"
After a few moments the Doctor's selective amnesia clears, and he remembers his massively embarassing previous incarnations - the shock of the sheer number of humilating memories that come flooding back nearly causes his brain to leap out of his skull for its own safety, but instead he just collapses on the floor in a cold sweat. All the while his Sixth Incarnation makes clumsy and insensitive pick-up lines.
When it becomes clear that simply meeting has nearly killed his future self, the Sixth Doctor sighs and begins searching around for the fridge, while number ten scrabbles to his feet. The sixth Doctor cheerfully explains that he was on the prowl for some high-class Edwardian tail fruitlessly once again, when he happened to find a photo of his unusually good-looking future self.
"So I thought I'd make out with MYSELF - after all it's clearly what I've wanted to do all these years..."
He goes on to say that to achieve this end, he has crashed his own TARDIS into the Tenth Doctor's, to create a dimensional instability that can destroy the entire Universe in five minutes - and will only leave once his future self agrees to some canoodling. The Tenth Doctor protests and theorises on the spot that maybe he can escape by eating a hole in the space-time continuum the size of Belgium.
"No, hold on - I've got no Pepto Bismol. Bad, bad idea!"
The Tenth Doctor's next plan seems to be to save himself by gnawing off his own face - or it may be just Tennant trying to convery ambivalence - but the Sixth Doctor attacks and the two find themselves embroiled in the most terrifying Benny Hill chase-scene ever! Eventually the TARDIS buckles again, and both Doctors fall to the floor. The Sixth Doctor cheerfully announces that a black hole is going to detonate any minute - AND NOTHING IN THE WORLD CAN STOP HIM NOW!!!
The Tenth Doctor leaps into action regardless, a dematerialises and rematerialises rapidly through an asteroid field, placing the asteroids in the TARDIS's orbit before aiming and launching them at a planetoid with the force to knock it out of orbit, slam into another planet and send it ricocheting into the black hole and blocking it instantly.
"You jammy bastard!" yells the Sixth Doctor
"Aha! I didn't do anything - I didn't have to! See, when you appeared I got your memories back of this incredibly humiliating experience of remembering me destroying two entire sentient alien races and their home planets just to avoid snuggling up to you, so I KNEW what to do and when to do it without any effort at all."
"ANOTHER Onthiological Paradox? Are you capable of working ANYTHING out for yourself? God, I can't believe my future self is so PATHETIC!"
The Sixth Doctor then repeatedly beats himself in the head with a hammer in a bid to wipe his memory of the encounter and thus create a big arse paradox. This causes the Tenth Doctor to smile wistfully.
"You know... I hated being you. I really did. Back when I first started, at the very beginning, I was always setting out to amaze people and bag as many women in ridiculous fashion as I could, like you do when you're young. And then I was you! And it was all lounging around and shouting at people and getting kicked out of gentlemen's clubs for indecent exposure and my voice going all squeaky when I shouted. I still do that, you bastard, I got that from you. I got some proper shoes, though. And a real sweet jacket. Snap. 'Cause you know what, Doctor? You were my least-favourite Doctor. And I'm nothing like you. Thank Christ."
The Sixth Doctor strangles him, but soon vanishes due to the TARDIS re-separating. The Tenth Doctor smiles in relief, and moves to the console to turn his shields back on as quickly as possible... only to find that the shielding circuits are missing!
The Sixth Doctor's voice cuts through the air, sneeringly "Oh, Doctor, I hope you didn't mind me taking a small souveneir? Arsehole!"
At that moment there is a terrible crash, and the TARDIS's wall crashes open, and the Tenth Doctor stares goggle-faced at... THE GIGANTIC FACE OF TOM BAKER!
"Any chance of a pint?"
"I said: 'Any chance of a pint?' "