Shanghainese for "stupid". 戆 in Cantonese also means an idiot or dense in the head. Standard Chinese means "blunt", "simple minded", "honest" aka country bumpkin.

1、戆gang4 rash; stupid; 2、戆zhuang4 simple; blunt, tactless; Two '戆s' in 戆头戆脑 are both pronounced gang4. http://www.zdic.net/z/1a/xs/6206.htm http://www.zdic.net/z/1a/js/6206.htm http://dictionaryq.com/chinese/ http://www.mdbg.net/chindict/chindict.php?page=worddict&wdrst;=0&wdqb;=%E6%88%86 Zdic.net is a overall mainly Chinese-Chinese and a little bit Chinese-English online dictionary.

不知道你们是查的什么词典，请看《高级汉语词典（电子版）》： 戇 gàng<形> [方]∶鲁莽,冒失 [rash]。如:戆言(言语鲁莽、冒失);戆激(鲁莽而激烈) 另见zhuàng 戆头戆脑 gàngtóu-gàngnǎo [act stupidly] 楞头楞脑;傻头傻脑 戇 zhuàng<形> 愚蠢(侧重于迂直、不知变通) [stupid] 戆,愚也。从心,赣声。——《说文》 悍戆好斗。——《荀子·大略》 狂惑戆陋之人。——《荀子·儒效》 然陵少戆,陈平可以助之。——《史记·高祖本纪》》 又如:戆冥(愚鲁昏昧);戆士(愚昧之人);戆大(方言。犹傻瓜);戆陋(愚昧浅陋);戆昧(愚昧);戆钝(愚笨) 憨厚而刚直 [blunt and tactless] 信着俺小叔莽戆多英勇。——元·佚名《千里独行》 又如:戆士(迂愚而刚直的人);戆介(迂直耿介);戆拙(迂直诚实) 另见gàng 戆直 zhuàngzhí [be blunt and tactless] 迂愚,刚直 所以，我个人觉得无论读gang还是读zhuang意思差不多，只是它们组合词语不同罢了，戆头戆脑中读gang4而其余几乎都读zhuang4.。并没有你们给出的那些区别。

this means sb looks not smart,,,in Taiwan we usually pronounce this in Taiwanese. 是一種台語的方言

gàng tóu gàng nǎo。 傻头傻脑的意思