Anything from IKEA (sorry, I just hate most of it).
Their tables are flimsy, often very square, often looking plastic-y and white. Usually hideous and lime green shelving wouldn't look out of place in an IKEA store.
I can see why people shop there as it is a cheap solution to a problem, but I think most of i looks terrible.
Their sofas are appalling too. I had to put up with one in a flat I rented a few years ago. The cushions slid off the fron constantly, the back cushions supported nothing so you couldn't really slouch back in them and they were too low.
I could go on.
Net curtains I don't particularly like, blinds are much better, but I can see why people would have them if their houses are right facing a busy street.
As for the feature wall, for the most part I quite like this. In my house I have two rooms like this, the second bedroom, with 3 of the 4 walls painted a light white colour and the 4th is a vivid purple. In my lounge we have some nice wall paper on two opposite wall with the rest painted. It would just look big, open and bland without it.
Oh, and carpets in bathrooms.
Laminate flooring when it is everywhere in the house, a rented place I lived in, every room was laminate, it was so annoying to sit on the sofa with your heels based on a really hard lounge floor. After two hours it was a right pain and I aren't a fan of rugs.
I'll expand on this post later today when I get back from work as I have loads more....pipework going to radiators going all over the walls - I know its easy to fix but pipework showing all over your walls looks horrible, the colour brown, I don't have too much of a problem with flooring tiles but they tend to be freezing cold to walk on throughout the year, knotted cheap skirting boards.
Downlighters/Recessed Spots in every room.
Fancy sockets/switches all over the house. White looks best in most rooms.
Mismatching sockets and switch styles tend to annoy me. I recently got rid of an expensive fancy switch for the cheapest bog standard white plastic type, purely because it didn't match the other cheap bog standard white plastic ones.