Narrow handlebars
Lack of bottle cage bosses - 2 pair for racing, 3 for touring
Seat post diameters all over the place
Uneven brake bridge height (looking at you, P15 Paramounts and Trek 710/716s!)
Single pivot side pull calipers
Special seat post binder bolts
Pre-standardized down tube shifter bosses
Non-sprung RD anchor bolts (not helping a general lack of chain tension possessed by older RDs)
Canti posts too narrow