Informal:
* Wordsmith: This term is usually used for someone who is skilled with language, but it can also be used sarcastically to describe someone who overuses complicated words.
* Logophile: This word literally means "lover of words," but it can also refer to someone who enjoys using complex vocabulary, potentially to the point of being ostentatious.
* Pedant: This term describes someone who shows off their knowledge, often in a pompous or annoying way.
* Pretentious: This describes someone who tries to appear more important or knowledgeable than they actually are, often by using unnecessarily complex language.
* Show-off: This is a general term for someone who wants to impress others, which could include using big words.
* Highfalutin: This word refers to something that is pretentious or pompous, and can be used to describe someone who uses overly complex language.
Formal:
* Sesquipedalian: This word refers to someone who uses long words, especially unnecessarily.
* Bombastic: This term describes someone who uses inflated language, often to appear more important than they are.
* Grandiloquent: This word refers to someone who uses an elevated and elaborate style of speaking, often to impress.
The best word to use will depend on the specific situation and the level of formality you want to convey.