Having been around for so long, the Doctor has been able to enlighten his Comapnions, as well as us the viewers, on a variety of subjects. Here is a place for the complete compilation of knowledge which the Doctor has bestowed.

To begin:

Bananas are good.

Watch out for blue boxes.

Scarves that can be wrapped three times around the neck and still drag the ground are cool.

Beware pepperpots with whisk attachments.

There's a great big universe out there ...

... but about two-thirds of all apocolypses and alien invasions take place in London, England, on planet Earth, in the early 21st century.

Mauve is more than just a color found in potpouri. It's also the color for danger.

It's a great big universe out there...

But somehow, a large proportion of it seems to bear a remarkable resemblance to a quarry in Wales.

Also, don't diss the sonic screwdriver.

Not only do neutrons have a polarity, they can flow.

(A reference to Three, in case the New Who fans are wondering. ;) )

Neutrons flow? huh. No wonder I failed high school physics.

If in doubt about something or it's origin give it a lick.

The French really know how to party.

Actually, not so much...

But somehow Three was always managing to "reverse the polarity of the neutron flow".

I guess the neutrons just like Time Lords or something. :D

If diplomacy fails, always make sure you have a supply of Nitro 9, a warrior woman with a knife or a tin dog set on stun at hand just in case.

Science is never really the way you learned it in school.

A majority of the universe have British accents. Except the Americans. Who have Canadian accents.

What now?

The delicate technology necessary for time and space travel can only be improved by judicious application of a rubber mallet at the precisely correct moment.

Wearing the same outfit every single day is not a sign of laziness or fashion idiocy, but rather a signature of your persona.

Always keep a concealed weapon on your person. Literally.

If you notice a word once on the radio, and then hear it again all day, it's not a coincidence. It's actually you, from the future, sending messages to yourself in a moment of omnipotence. Pay attention.

If the Doctor mispronounces your name, don't be offended, that's probably just an Alternate Universe you he's talking about.

That you can use a 20th-century reel-to-reel tape recorder to detect timey-wimey stuff. Though you have to be careful of detonating chickens.

Don't look away and don't blink.

You can tell a lot about a thing simply by licking it.


Oh, and it's always handy to have a spade around in case you need to do some digging.

Things can always be more sonic.

When the missus and the ex meet, it's best to stay away. They will make fun of you.

Stay at least three paces back from a companion's Mother. That way they can't reach.

Lots of planets have a north. And glib, throwaway one liners are a perfect way of explaining things that don't make sense.

When you come across something you don't understand, don't say it's "magic." Use a bunch of nonsensical technobabble.

Reality TV will never go out of style.

Always brush up on your sword fighting. You never know if a battle to the death with an alien or an android or your arch-nemesis will come up.

Don't tick off Queen Victoria. She'll get her revenge, even if it's a couple hundred years later.

If you're employed by a mad scientist who tells you he plans to bypass the international governing body on ethics, don't then announce that it's your duty to inform them. Particularly when your boss' monstrous creation is standing directly behind you.

Similarly, if he says, "And how do you plan to do that ... from beyond the grave?", don't stand there stammering, "Wh-what?". It's pretty clear what that means. RUN!!

An MRI machine can fry the brain stems of humans but leave computers working perfectly normal.

And a sonic sounding thing near a sound system will make Santa robots shake like a bowl full of jelly.

When in doubt, pull the red wire. And always wait five and a half hours.

There are worlds out there where the sky is burning, and the sea's asleep, and the rivers dream; people made of smoke and cities made of song. Somewhere there's danger, somewhere there's injustice, somewhere else the tea's getting cold.

When going to meet your idol, put on your best jumper.

Swear by rubber soles.

When putting your time machine's console together, don't skimp on the glue/epoxy. Otherwise, your assistant might rip it open and abosrb the entire time vortex.

You can make paradoxes, but only for cheap tricks.

Don't let the most powerful person on the planet see you grinning wildly at a werewolf. You have no idea how it will change the timeline.

Where there's life, there's hope.

It's never too late.

Don't wear a Bluetooth.

Long coats look smashing.

And have handy deep pockets too!

Bananas are good. (Although I have to disagree with the Doctor here!)

If you hear a word or phrase repeated often, it'll probably be very important later on. It might even follow you to a beach in Norway.

Almost everything is bigger on the inside.

Or even just once. He only said "A footprint is not shaped like a boot" at that park before he went to Torchwood and found the Cybermen.

All "supernatural" occurrances- such as ghosts, zombies, werewolves and witches- are actually aliens or alien technology.

Chucks are an appropriate shoe for any attire.

I think I'd worked that one out for myself.

You can create one hell of an explosion using a school science lab's worth of gas taps and a plug socket.

Sometimes, six words are all you need to change the course of future events.

Ancient High Gallifreyan looks an awful lot like Greek (ref. the episode The Five Doctors).

The Mona Lisa is a fake (City of Death).

Speak softly and carry a bottomless bag of jellybabies.

Global communication monopolies are bad (Cybus, Archangel...)

Daleks are like cockroaches: you can spray them, and stomp on them, and blow up their planet, but you will never get rid of all of them.

Heee.

Don't be annoyed if you meet someone claiming to be you. They are not a fan - they are you.

Never underestimate the value of a tux and a good pair of sensible shoes.

References to classic literature involving the "unknown" are a plus - including the word, "Expeliarmus."

S04E03: Drinking alien DNA/stem cells/Ood graft suspended in biological compound will turn you into an alien.