I suppose it's worth noting that directing "abusive, vulgar, or offensive" language at a supervisor is not always disqualifying - the Commonwealth Court noted precedent holding that the employee may still be eligible for unemployment compensation if the language was provoked or de minimis.
Putting on my employer-side hat, employers should know that when employees are engaged in protected concerted activity (acting together to address the terms and condition of their employment), then their conduct is protected by the NLRA. Employees do not lose that protection just because their language is a little coarse. That said, there is a (not very clear) line that employees cannot cross without losing that protection.
HT: Matt McClenahen for the pointer.