always saying the wrong thing; chronic foot-in-mouth
Describes a person who frequently makes verbal blunders or inappropriate remarks. Often used humorously or critically.
He always says the wrong thing and freezes the atmosphere at every meeting.
That politician is famous for constantly putting his foot in his mouth.
失言 refers to a single verbal gaffe, while 年中失言 describes a habitual tendency to make such gaffes.
Compound of 年中 (ねんじゅう, 'all year round, always') and 失言 (しつげん, 'verbal gaffe'). The exact origin is uncertain, but it likely emerged as a colloquial expression for someone who habitually says the wrong thing.