To a Muslim showing the bottom of your feet is a serious insult. I think Barrack is saying fuck you to the American people in that pic.
Normally I would say fuck off but I am feeling nice tonight. I am sure you know how to use Google?
https://www.telegraph.co.uk/news/worldnews/middleeast/iraq/3776970/Arab-culture-the-insult-of-the-shoe.html