oblivious
Meaning: lacking consciousness or awareness of something
Usage: Oblivious to the burning smell emanating from the kitchen, my father did not notice that the rolls in the oven were burned until much too late.
obtuse
Meaning: lacking quickness of sensibility or intellect
Usage: The obtuse student missed the obvious hint in the teacher’s question.
complacency
Meaning: self-satisfied ignorance of danger
Usage: Colin tried to shock his friends out of their complacency by painting a frightening picture of what might happen to them.