This African supervisor should be fired. What is it with immigrants who come to this country, find a way of life vastly superior to the countries from which they fled, and then show their contempt for the USA? This should be a deportable offense.
Nope, not so. The freedom to be offensive needs to protected, so long as the potential deportee came here under the rules and has been law abiding.
But a good, solid shunning is in order. Who wants to interact with such an individual, anyway?