The most recent instagram post from Donald Trump has been flooded with thousands of replies saying "cabeza de pichi" or "cabeza‘e pichí", almost all written by Chileans. This originates from comedian Felipe Avello, who joked at the Viña del Mar Festival about writing this very phrase on Trump’s Intagram.
"Cabeza ‘e pichí" is a chileanism, a slur referring to a person with light, blond, or red hair. The literal translation is "piss face" or "piss head", comparing the person's hair colour to the colour of urine.
The phrase went viral mostly because, apart from simply being funny, it is an act of defiance and irreverence to an authority figure who is held in very low regard and happens to be leader of one of the greatest powers in the world.
Update 19:04 (GTM -4):
Because of the sheer number of replies, the account had to shut down comments.