Sure, if you are working in government, want to show deference to the office or office-holder, or cretainly if you are part of the active military, Joe's answer and the Wiki page hold. But is that proper? America also has a fine and noble tradition of booing, heckling and generally reminding whomever the jackwagon is in office that they actually works for us. So feel free to call him or her whatever you like. It's just as proper and more American.
The better view may be that America is a country built on dissent, which protects protests and that the act of booing is an exercise in free democracy. And even and especially as the current administration veers more towards a theocracy, we should perhaps cordon off the machinations of the government and of the pieties of faith. Our law is not Torah, but the constitution and, as mentioned above, it is advisable to correct someone who takes to “scorning the words.”
