Nine Out of Ten Doctors Agree/WMG

All ten doctors are Time Lords
C'mon, someone had to say it.

The nine doctors that are agreeing are talking about sixth's coat.

 * No, it's the fourth's.
 * No, it's Eleventh's fez.

So what does the eleventh do?

 * He promptly fucks off so the others can finish their conversation.
 * No, they bribed him to leave because he agreed with Tenth and 90% approval is better than 81%.
 * He's  and thus unavailable for comment.

The 10th doctor's a prick
He knows that the other 9 are right, he just likes to disagree.

The 10th doctor got hit in the head and fell on the "no" button by mistake.
They showed it in a Trident commercial, it must be true! (though they had 4 out of 5)

The 10th doctor is a Ph.D.
See, for instance, "Dr." Gillian McKeith.

All the doctors are the original 10 doctors in Doctor Who.
To go with the above theory about how they're Time Lords.

The 10th doctor doesn't really believe what he says
The other 9 hate him and are just disagreeing out of spite. So #10 has started proposing leeches, blood-letting, and cocaine for everything so that the other 9 will go disagree and pick the smart alternative.

...that this really isn't their field of study
They just kinda hoped you wouldn't press the issue.

The "tenth" doctor is actually the sixth.
The Colin Baker Doctor seems the most likely to be contrarian to his other selves just for the sake of it. After all, he wore the coat just to piss people off.