Formal:
* Affected: This emphasizes the artificiality of the behavior.
* Pompous: This suggests a self-important and inflated sense of self.
* Grandiose: This implies an exaggerated sense of importance or scale.
* Ostentatious: This highlights the showy or extravagant nature of the behavior.
* Arrogant: This emphasizes the feeling of superiority.
* Supercilious: This suggests a disdainful or patronizing attitude.
Informal:
* Show-offy: This focuses on the desire to impress.
* Poser: This suggests someone who is trying to appear something they are not.
* Snooty: This implies a condescending attitude.
* Highfalutin': This implies using elaborate or overly complicated language.
* Smug: This suggests self-satisfaction and a sense of superiority.
* Stuck-up: This is a more direct and informal way of saying someone is pretentious.
The best synonym depends on the context and the specific tone you want to convey.