fat·head 
/ˈfætˌhɛd/ noun
plural fat·heads /ˈfætˌhɛd/ noun [count] informal : a stupid person
▪ Don't be such a fathead!
▪ Don't be such a fathead!
— fat·head·ed /ˈfætˈhɛdəd/ adjective [more fatheaded; most fatheaded]
▪ a fat-headed [=stupid] idea/person
/ˈfætˈhɛdəd/ adjective [more fatheaded; most fatheaded] ▪ a fat-headed [=stupid] idea/person
— fat·head·ed·ness noun [noncount]
