Humorous:
* Malapropism master: This is a playful term, referring to the person's tendency to misuse words in a funny way, much like the character Mrs. Malaprop in the play "The Rivals."
* Wordsmith in training: This implies they are trying to use big words but haven't mastered them yet.
* Lexical adventurer: This is a lighthearted way to describe someone who is exploring language but isn't quite there yet.
More critical:
* Pretentious: This implies the person is trying to sound smarter than they are.
* Pedantic: This suggests they are overly concerned with using complex language, even if it doesn't make sense.
* Obscurantist: This refers to someone who deliberately uses obscure language to confuse or mislead.
* Sesquipedalian: While this word itself means "using long words," it can be used ironically to describe someone who uses long words incorrectly.
Neutral:
* Someone who misuses vocabulary: This is a straightforward and accurate description.
* Someone who struggles with word choice: This is a more gentle way to say they have difficulties using words correctly.
Ultimately, the best way to describe someone who uses big words incorrectly depends on the specific situation and your intention.