Collocations for incompetent - adj.

appear, be
consider sb/sth, deem sb/sth (formal)
I know my boss considers me incompetent.

criminally, grossly
a grossly incompetent piece of reporting

hopelessly
completely, totally, utterly
socially, technically
mentally
legally
the medical treatment of legally incompetent patients (= those who are not able to give legal consent)

at
He is utterly incompetent at his job.

Incompetent is used with these nouns:
teacher