totally/highly/completely etc irresponsible
When it comes to money, Dan is completely irresponsible.
it is irresponsible (for somebody) to do something
It would be irresponsible not to turn up for work without calling.
It was highly irresponsible of him to leave the children on their own in the pool.
He was acting totally irresponsibly.
—irresponsibility noun [uncountable]