Pyracantha! Lovely berries but a nightmare to prune and the flowers give me hay-fever! I quite agree with the dislike of salmon geraniums - YUK! Double daffodils - WHY???? Carex pendula - really attractive until you realise it has self-seeded and taken over your entire garden! But Ground Elder is my No.1 most hated, I eventually gave up and moved house!!
I love orchids of all kinds, roses, sweet peas, honeysuckle, ferns, jungly plants, carnivorous plants, even humble daisies.