09:09 Jul 20 

'Bighead' was used quite a lot by schoolchildren during my schooldays.

03:18 Jul 20 

When someone says for a person "την έχει ψωνίσει" , it means he is mentally absent, he is nuts (another way to express this is : του λασκάρισε η βίδα). However, always depending on the broader context "την έχει ψωνίσει" can mean that someone reacts illogically /takes illogical decisions.
Saying that someone is "ψώνιο" or "ψωνάρα" means that his acts and decisions are far away different compared to the ones a reasonable person takes; in that case, bighead (UK), swellhead (US), show-off, crackpot express the idea.

14:09 Jul 19 

A friend, who returned from Greece recently, explained that ψωνάρα means (roughly) an empty-headed person, but then she modified this by saying that really it means a person who is mentally "absent". I'm really not sure which meaning is uppermost: bighead/swellhead, or mentally "not quite there".