1. sweaters with pilling (unless you can shave the pills off)
2. shirts with snags (especially in poly). (For snags on sweaters, just turn the sweater inside out & pull the snag through with tweezers)
3. anything with holes that can't be repaired (unless it's jeans--then the holes are still cool. Or unless you can cut off that part to create something new, or you know someone like Monica who can repair ripped sweaters. Many drycleaners/seamstresses can also repair small holes in sweaters, even in cashmere)
4. white shirts that have yellowed or anything with a permanent stain (try a drycleaner before giving up--sometimes they work magic). In particular, take a look at your cuffs--dingy cuffs are a revealing sign it's time to let it go.
1 item to keep: too-short pants. If your pants are too short, SHORTEN them to a capri or ankle length. Even some men are wearing some pants short these days--see post from Peter Lappin about shorter hem lengths on men's pants here
What have I left out?