pompous
Acting overly important and showing off in an annoying way.
Pompous describes someone who acts overly impressed with themselves and wants everyone else to be impressed too. A pompous person uses big words when simple ones would work better, brags about their achievements constantly, and treats others as if they're not as smart or important.
Imagine a student who wins one spelling bee and then spends weeks telling everyone how brilliant they are, using unnecessarily complicated words and correcting other people's grammar in a superior tone. That's pompous behavior. Or picture a dinner guest who monopolizes the conversation to discuss their accomplishments, never asking others about their lives. They're being pompous.
The word carries a clear negative feeling. While confidence means believing in yourself, pomposity means showing off that belief in ways that make others uncomfortable. A pompous speech might be filled with fancy vocabulary designed to impress rather than communicate. A pompous leader might surround themselves with expensive decorations and insist on elaborate titles.
You might hear someone described as pompous or accused of pomposity (the noun form). A particularly over-the-top display might be called pompous nonsense.