There are several such words in Cantonese that for a long time, my friends and I could not satisfactorily translate into English.

無聊(mo liu) - this partially means 'inane', but the English word doesn't give the full meaning.

無奈(mo noi) - best expressed by -_- or perhaps ^_^;. The usual English term 'to sweat-drop' is gacked from Japanese anime where characters do this when they are mo noi, usually accompanied by a blue/black cloud around their head plus a drop of sweat/several straight lines.