Green’s Dictionary of Slang

1. old or comfortable, informal clothes or shoes.

1966		Current Sl. I:3 4/1: Grubs, n. Old, comfortable clothes; esp. cut-off jeans.
1968		H. Sebold Adolescence 223: In California in 1966, a preference for battered-looking sneakers evolved [...] called [...] ‘grubbies’ by teen-agers.
1975		G. Underwood ‘Razorback Sl.’ in AS L:1/2 54: grubbies ‘slopp clothes’.
1998		J.E. Tada More Precious Than Silver 21: Friends from the congregation set aside a Saturday, donned their grubbies, and brought brushes, ladders, and paint to spiff up the place.
2002		G.M. Lockwood Complete Idiot’s Guide to Organizing Your Life 171: Put a limit on clothes you keep as ‘grubbies’ for grungy jobs.

2. smelly or dirty feet.

2000

Eble Campus Sl. Spring.