Personal selections, in no particular order and all based on experience and the idea of actually living and working there.
London, UK - I actually lived there for four minutes once.
Joensuu, Finland - Beautiful surrounding area but the city was kind of scary.
Oxford, UK - Lived there for three years, unconnected to the academic aspects of the place. Hated everything about it.
Dublin, Ireland - Apart from Guinness and a nice art gallery, it depressed me. It's probably
really bad now.
Charleroi, Belgium - People who know Belgium will know what I mean. Charleroi is why man invented beltways/ring roads.
See also: great thread on skyscrapercity.com:
Ugliest City in Western Europe