Informal and humorous:
* Sesquipedalian: This literally means "having a foot and a half long" and refers to using long words. It's a fun, playful term.
* Logophile: Someone who loves words, but might use them excessively.
* Wordsmith: While not specifically about using big words, it can imply someone who enjoys using elaborate language.
* Show-off: This implies the person is using big words to impress rather than communicate effectively.
More formal and critical:
* Pretentious: This suggests the person is trying to sound more intelligent or sophisticated than they are.
* Pedantic: This describes someone who is overly concerned with small details, including the use of unnecessarily complicated language.
* Obscurantist: This term suggests the person is intentionally using complex language to confuse or mislead.
* Grandiloquent: This describes someone who uses bombastic language, often in a way that's self-important and pretentious.
Ultimately, the best term depends on the specific situation and the tone you want to convey.