My favorite address WTF (from when I worked at a startup that managed deliveries) was an apartment building in New York City. If you tried to geocode the full address of an individual apartment (123 Someplace St Unit 789, etc) it would fail - but an address without the unit would succeed!

This was particularly weird because normally the geocoder was fine with bogus unit numbers (eg on obvious single-family homes) but fell over in just this one case...