noun, na-adjective
Describes a person's boastful or swaggering attitude; often used with する to mean 'to brag' or 'to show off'.
彼はいつも大威張りで自分の成功を話す。
He always talks about his success in a bragging way.
大威張りするのはやめてください。
Please stop showing off.
Compound of 大 (おお, 'big') + 威張り (いばり, 'boasting'), the noun form of 威張る (いばる, 'to be arrogant'). The exact historical derivation is uncertain, but the word likely emerged as an emphatic expression for boastful behavior.