Green’s Dictionary of Slang

lunch adj.

[out to lunch adj.]

1. stupid, foolish, crazy.

[US] ‘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.

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’.