fast asleep and unaware of surroundings
Yojijukugo describing someone who is sound asleep and oblivious to what is happening around them. Often used in the phrase 白河夜船を決め込む (to pretend to be fast asleep).
He was fast asleep during the meeting and didn't hear anything.
He pretended to be fast asleep and acted like he didn't know.
know-it-all attitude; pretending to know everything
Rare, possibly archaic sense. Refers to a person who acts as if they know everything, often while actually being ignorant. The connection to the literal meaning is unclear; may derive from a story where someone pretended to have traveled to Kyoto by boat on the Shirakawa River while actually asleep.
His know-it-all attitude is annoying.
Rare variant combining 川 and 舟.