What a shock! I was just watching Frasier reruns on Netflix earlier this afternoon. Mahoney's performance as the irascible beer drinking father having to contend with his pompous, sherry drinking sons was just perfect.
I read somewhere that contrary to his character in Frasier, Mahoney was very refined. In fact, David Hyde Pierce consulted with him about fine wine in preparation for his role as Niles.
Rest in peace, John Mahoney.