That rechargeable Magic Mouse, definitely. Dumbest idea to put the charging port at the bottom. Also probably considered to be one of Ive's masterpiece...
Butterfly keyboard, also an obvious, to the point that Apple ditched it.
iPhone 6/6 Plus. Despite the first entry into phablets and I think still the bestselling iPhone ever, the choice of material (bendgate) and paltry 1GB of RAM still put it on my bad Apple list.
Base 21" iMacs. The fact that the non-BTO base models come with plain slow 5400rpm spinning drive (except on the highest end), and the fact that it's not easily user upgradeable, really contradicts Apple's motto for making "the best product." Putting a Ferrari on bicycle wheels won't get it very far.
Also, all iMacs and Mac minis, for making it very hard to almost impossible for lay users to simply upgrade the RAM and hard-drive. I remember the old plastic MacBooks where the RAM and hard drive were extremely easy to access and replace. I can kinda understand with laptops being less accessible today due to the form factor (many Windows laptops don't have it any easier), but on desktops? Come on. It would be somewhat acceptable if Apple use SSD as standard on all iMacs, but they don't.