How can I say "why are you making a duck face" in Russian?
That sentence makes me smile. Sure enough, to its credit, Urban Dictionary, being an open resource, at the same time would unlikely be considered the most trustworthy one on the web in this respect, and yet, here is an entry I like:"A facial expression utilized by attention-seeking teenage girls in which they push their lips outward and upward to give the appearance of large, pouty lips. Amanda Fuchs makes a duckface in all of her profile pictures."
Some coquetry given, I would suggest something like Милая, к чему такое"поцелуйное"личико? or Ты уверена, что твоя утиная гримаска здесь уместна?
Internet yields another sample:"...сбегала к зеркалу, скроила утиную морду - реально кажется. что суперсекси..." which indicates that the English authentic(?), not sure about its etymology, phrase has been successfully infiltrating the Russian everyday speech).
Young people mostly use a word "дакфейс" (read exactly like englich 'duck face' ), specially when facing a phenomenon of a young woman wearing this facial expression on a photo. A verb would be "сделать дакфейс" (perfect form), and here is another common example:
На новом фото Катя опять с дакфейсом
(Katya makes a duck face on her photo again)
Other examples in this thread feel a bit odd to me. They are correct indeed but suit older people or some official speech better (f.e. journal, book), however, the duck face phenomenon is clearly out of the list of topics discussed in journals or between politics.