Because he's the Doctor. He's a Time Lord. He's from Gallifrey, in the constellation of Casterberus. He's 903 years old. He's the man who's gonna save your lives, and all six billion on the planet below.
Because no one's got a problem with that.
Because he never changes.
Because Donna's got a hat box.
Because the fat just walked away.
Because he just wants A mate.
Because he is Spartacus. And so is she.
Because they're so not a couple.
Because he fought her off with a water pistol.
Because he got clever in Latin.
Because 'TARDIS, Time Lord, yeah!'
Because 'Donna, Human, no!'
Because they turned him into an Ood. Seriously.
Because every song must end.
Because at least they've got quality handcuffs.
Because, to an Ood, Donna looks single.
Because he came 'intruder window'
Because it's not easy being clever.
Because of course he didn't turn Martha into a soldier.
Because the Doctor's a dumbo.
Because he's a great big outer space dunce.
Because he's also a prawn.
Because of 'Staal the Not-quite-so-undefeated-anymore-but-never-mind.'
Because when he put on a gas mask, he said "Are you my mummy?"
Because Donna's got three fingers.
Because he's really glad he didn't say 'belittle'.
Because she's a Jenny-rated anomaly.
Because she survived after all.
Because she was too much like him.
Because she has a lot of running to do.
Because they're saving Donna's 'womanly wiles'
for later. In case of emergency.
Because 'there's an outrageous amount of running involved'
Because he can tell what year it is just by smelling.
Because salt is too salty.
Because Harvey Wallbanger is one word.
Because of all of the references to Agatha Christie's novels and stories.
Because there's no Noddy.
Because Donna commands it to be otherwise. Scotland Yard. Pip pip.
Because when she says giant, she doesn't mean big, she means flippin' enormous!
Because she's ever so plucky!
Because he points and laughs at archaeologists.
Because he never lands on a Sunday. Sundays are boring.
Because he's a pretty boy.
(Because we didn't need a professor to tell us that!)
Because he needs a bigger head.
Because of the 'spoilers'
Because if he dies, she'll kill him.
Because he's always all right.
Because he'll try his hardest not to die.
Because... hey! Who turned out the lights?
Because it's chicken and
Because he's the Doctor, he's very clever.
Because he says 'allons-y'
and 'molto bene'
Because the square root of pi is 1.772453850905516027298167483341. Wow.
Because 'isn't that wizard'
Because Rose called her brilliant too.
Because, it's true; he did have some great hair.
Because of course Donna's special.
Because we all secretly love Bad Wolf.
Because Jack, Ianto and Gwen are back!
Because the Daleks are back!
Because Sarah Jane and Luke are back!
Because Jackie is back!
Because Martha is back!
Because Rose is back!
Because Mickey's back, but he's still a bit of an idiot.
Because Harriet Jones is back, and we haven't forgotten who she is.
Because it's not Cheesecake, it's Beefcake.
Because Caan is the only Dalek that can giggle.
Because Davros is the Dalek's pet.
Because the Doctor can speak Judoon.
Because the Doctor and Rose ran to each other.
Because Daleks do not accept apologies.
Because it's an outer space Facebook!
Because we all love it when the Doctor says 'The lost moon of Poosh'.
Because of Ianto's face when he watches Paul O'Grady.
Because THERE ARE TWO DOCTORS.
Because the Ood knew all along.
Because we all know what Jack is thinking.
Because Jackie can't help.
Because "There goes the Time Lock!"
Because Jack thought he'd finally got rid of Mickey.
Because "Don't blink, do you remember that?"
Because it makes a noise, that makes it sonic.
Because Tethered Aerial Release Developed in Style. Good TARDIS.
Because the Cybermen are getting lippy.
Because it's all fantastic!