Green’s Dictionary of Slang

butter adj.1

also butters
[butt n.1 (1a) + ? play on cheesy adj.2 (4); ? note bhutto n.]

1. [1980s+] (orig. US campus) of an object or person, unfashionable, unsophisticated; also as n.

2. [1990s+] of a woman, unattractive.