seems redundant given that the c̶o̶u̶r̶t̶ NLRB siding with the employee suggests that even in the US employees are likely protected in this case, but interestingly i feel this one is undecided, because insults are taken quite seriously in some european countries.

from germany i know that whether an insult is grounds for firing someone depends on the regular interaction the two people have, so if you take a company of rednecks (to employ a stereotype), a redneck employee calling their redneck boss some typical redneck insult would be interpreted as acceptable, and make any firing based on that illegal. but if the same insult is used by a lawyer in a law firm from a big city, then suddenly that same insult is a valid reason to get fired.

(edit: rephrase and replace court with NLRB)