Anything using the Borg set with visuals enabled.

The Luna class iritates me, as looks good from some angles, but looks like a dog dragging itself across a carpet from others.

The golfball science ships qualify

Trident class Science ship - looks like a giant boot or a Vacuum cleaner or something.

And I'm sorry - I realise that this goes against popular opinion, and I don't hate it, but I find the Defiant class completely uninspiring. Again, this is my, personal, opinion, but it's nothing more than a saucer section with a nose-job and two nacelles shoved into it's side as an afterthought. I am aware of the supposed 'low profile' blah blah blah reasoning behind it but I'm sorry, I just don't like it much. Considering some of the concept art/designs for the class the end product just looks lazy and rushed.

Outside of STO - some of the DS9 Dominion war kitbashes were awful.