inept

Not able to do something; not proficient; displaying incompetence.

As a waiter, he was inept, so they put him in the kitchen.

Unfit; unsuitable.

The bungled phrase, the slipshod paragraph, the inept metaphor, the irrelevant excursion, the disproportionate development, the feeble conclusion, are indeed all failures of meaning, and the more poetically ambitious the verbal structure in which they occur, the deeper and more substantive the failure may be.