The dinner party was ruined by the host's excessive stuffiness and lack of warmth.

stuffiness 是由形容词 stuffy（古板的、沉闷的）加上名词后缀 -ness 构成的名词形式。stuffy 本意是"空气不流通的"，引申为"思想僵化的、拘谨的"。stuffiness 在这里指"古板拘谨的状态或特质"。