To be fair, I found pictures of W. and Gerald Ford with their feet up on the desk too. But I don't think any previous president ever did it with disdain. When the current one does it, I picture a dog lifting its leg. Not only to soil that which he holds in contempt, but also to make sure everyone knows he has marked his territory.
I think when previous presidents had photo ops with their feet on the desk, it was supposed to convey this "casual competence" image. And I don't like that, either. I don't like any president doing it, for any reason. But there are definitely degrees of affront, and the current one positively revels in pegging the meter at every opportunity.