have one's head up one's ass

have one's head up one's ass (third-person singular simple present has one's head up one's ass, present participle having one's head up one's ass, simple past and past participle had one's head up one's ass)

1. (slang, derogatory, Canada, US, vulgar) To be oblivious to the real state of things, from either stupidity or stubbornness.

• get one's head out of one's ass

• asshat
• think the sun shines out of someone's arse
• up one's own ass