Green’s Dictionary of Slang

1. stupid, foolish, crazy.

1963

‘Miscellany’ in AS XXXVIII:2 159: University of Buffalo undergraduates have used lunch as an adjective, synonymous with useless [...] [A] University of Buffalo...informant explained...that ‘a lunch guy might as well be out to lunch for all the good he’s doing anyone where he is’.

2. good, excellent, admirable.

1993–2003

Urban Dict. 🌐 lunch Lunch can also be used as an adjective. The definition is similar to the meaning of ‘cool’ or, as in the olden days, ‘hip’. Man...that movie was ‘lunch’.