Just like the Brown suit etc. Even though there are pics with other presidents with their feet on the desks, his was the only one deemed to be "disrespectful".
http://www.washingtontimes.com/news/2013/sep/4/obamas-feet-oval-office-desk-sends-shockwaves-arou/
https://www.mediaite.com/online/obama-put-his-feet-on-oval-office-desk-and-people-are-outraged/
And you and I both know if he was throwing stuff at white middle americans that had just lost everything, Fox News and Republicans would've had a stroke. Let's be serious...