nO STOP THIS IS NOT OK my brother lost his **** when 11 regenerated "I've got new kidneys... I don't like the color!"
They say the Doctor regenerates what he needs most. Matt Smith (in the newest episode) pulled off a wig and had no eyebrows, then stated his eyebrows were weak. Thus, thirteen - Capaldi - naturally had thick and bushy eyebrows.
Well, in 'The Day Of The Doctor' you see a shot of his eyes and eyebrows, which look to be pretty bushy. Also, Capaldi naturally has those eyebrows, so note how the 'weak eyebrows' comment was made AFTER Capaldi was selected to be Doctor; therefore it's probably not.
Who is the "his" when you mentioned "his eyebrows" in the Day of the Doctor? If it's Matt Smith, then why would the Doctor need better eyebrows?
His references Capaldi. Well, here is either an example of Moffat being an arse and not holding together a decent plot (since there are a multitude of other things that the Doctor needs), or it's something to do with it being a [SPOILERS!!] thirteenth regeneration, therefore not natural. [/end spoilers!] This also plays into the part at the end when Capaldi remembers certain things, such as having 'new' kidneys (which means he remembers about regenerating or something because otherwise they wouldn't be 'new',) but not others, such as how to fly the TARDIS. All in all, The Day of the Doctor makes for an extremely interesting new series!
That last "all in all" sentence, Dave, sounded like one of those conclusion paragraphs that you write for an essay that you have neither the patience nor the interest to spend much fine on.
Also, Matt Smith had no eyebrows, and also I have no clue what you are complaining about Moffat for...