feigned ignorance; pretending not to know
Abbreviation of the set phrase 知らぬ顔の半兵衛, used to describe someone who acts as if they know nothing about a matter.
See also: 知らぬ顔の半兵衛
There is a phrase 'shiranu kao no Hanbee' (feigning ignorance like Hanbee).
When things get awkward, he quickly pretends not to know anything.
Abbreviation of the phrase 知らぬ顔の半兵衛. The name 半兵衛 is a common male given name from the Edo period, used here as a generic personification of someone who pretends not to know.