Green’s Dictionary of Slang

1. dull, stupid, absent-minded.

1964		in Sat. Eve. Post 22 Feb. 73: Having to share his new campus with a good number of lunchy undesirables [HDAS].
1974		Eble Campus Sl. Mar. 4: lunchy [...] What are you doing, you lunchy?
1996		Eble Sl. and Sociability 33: Another frequently used suffix is adjective-forming y [...] College slang has dorky, fratty, freaky, geeky, grooty, lunchy, spacey, squirrelly, and others.

2. carefree, light-hearted, jokey.

1967		Current Sl. II:1 4: Lunchy, adj. Careless, as if the performer were ‘out to lunch’.
1975		G. Underwood ‘Razorback Sl.’ in AS L:1/2 62: My roommate is positively lunchy today.

3. unfashionable, out of style, e.g. He looks so lunchy wearing that bow tie.

1975

G.N. Underwood ‘Razorback Sl.’ AS L 62: Lunchy [...] 3. out of style.