[thrill]

Avoid personal accusations of incompetence ("Dave in Marketing is a waste of a coveted cubicle seat!") and give your honest opinions backed up where possible with data ("The attached measures indicate our marketing effectiveness ranks in the bottom quartile per dollar spend compared to similarly sized companies in similar markets"). Reality will exist somewhere between those extremes since you likely don't have extensive data and likely know quite well of personal incompetence.

Treat this as an exercise in clear thinking and expression.