to be at the core.

'Estar hasta las narices' is a Spanish idiomatic expression which does not translate directly into English but the equivalent might be to say that you are 'fed up' or 'to have had it up to here'. It is not meant to literally mean 'be at the core'. It is typically used to show a high level of frustration or annoyance, usually directed at a specific situation or person. Translated word-for-word in English it means 'to be up to the noses', which makes little sense in English, hence it is clearly idiomatic in nature.