Suede: the production sounds so thin, even on 'Dog Man Star' - an album I worshipped when it came out and a long time after. A lot of '90s British indie in general, but I feel more disappointed about how Suede sound to me now. (I note that for their best-of they remixed certain tracks, most notably putting a beefier vocal on 'Trash'.)
Any mid-'80s UK big-name chart music made on a Fairlight with that flat, artificial sound. I'm thinking especially of Peter Gabriel, Duran Duran, Nik Kershaw, all the stuff that was dominating the pop charts at the time. The exception is 'Hounds Of Love' because Kate Bush = genius and could make a washing machine sound wonderful.
All disco, except Chic/Sister Sledge and Donna Summer/Giorgio Moroder's 'I Feel Love'. (Are Chic playing at Electric Picnic? If so, FFS go and see them!)
And I guess few people, if any, listen to pre-'65 Beatles i.e. anything before 'Help' and 'Rubber Soul'.