威張る

1. Origins, structure, and basic meaning

• Structure: 威張る（いばる） means acting as though one is important or superior, behaving arrogantly, or showing off.
• Basic usage: 役職が上だからといって威張ってはいけない concerns arrogance based on rank; 勝ったことがうれしくて少し威張った describes showing off a little after a win.

2. Common pitfalls and similar expressions

• Attitude rather than words
  • 自慢する focuses on boasting about one's strengths or achievements. 威張る emphasizes a self-important manner or an overbearing attitude toward others, even without a specific spoken boast.
• The strength of criticism depends on context
  • The first example warns against a superior's attitude, while the second describes a happy younger brother showing off 少し. Both involve self-importance, but the strength of the criticism varies with context.