The term 'thickhead' is informal and can offend someone if used seriously.

Colloquial Insult

Don't use 'thickhead' in formal settings, such as job interviews or official documents.

Avoid in Formality

Sometimes 'thickhead' is used between friends as a joking rebuke.

Know 'thickhead' refers to a bird family when discussing ornithology or Australian wildlife.

Recognize that 'thickhead' as a bird mainly pertains to Australia and Papua New Guinea.

Understand that 'thickhead' isn't an insult when talking about birds; it's a proper noun.