Fodera. One reason for that is because Anthony Jackson's dismissive and arrogant article in Bass Player magazine in the early/mid 1990s turned me off (I was strong willed teen back then), and made me associate Fodera with snooty elitism. I once played a Fodera bass, and while it was one of the best instruments I ever put my hands on... it felt soulless and sterile to me. I much preferred the bass I had at home. And I still don't like Fodera or Anthony Jackson.
That's also why I'll never GAS for a Jeff Berlin sig 5-string, despite it having the kind of specs I like. The man is a monster player, but his dismissive arrogance and snooty elitism disgust me and I don't want to play a bass that gives me that kind of negative mental association.
I'll also never GAS for a Spector MK-5 Pro, despite it having the kind of specs I like. I'm sure Mike Kroger is a nice enough dude, but I think Nickelback is an absolute garbage band and I don't want to play a bass associated with something I dislike.
Fender. There are so many amazing builders out there doing Fender better than Fender, that the supposed "real McCoy" holds no sway for me. Plus, they're ubiquitous and I like to have instruments that are unique. Something that not everyone and their dog is playing.
Anything with a spalted maple top. Those look like wood rot to me and that's ugly.
Any active bass that does not have an easy access battery compartment. The ashtray-style ones on Japanese ESP basses are really slick. Also, any active bass that doesn't have full passive bypass. Because nothing's worse than your battery dying on a gig and either you not having a spare or having to unscrew cavity plates, wasting precious time.
Headless basses. The look broken to me and their design limits my string choices. I especially dislike Steinbergers. Where's the body? I want a bass with a body that has curves and horns.
Extended scale basses (e.g. Dingwall.) Praise that 37" scale low B all you want, but I don't like basses that limit my available string options.
Rickenbacker. Fine basses that have killed on may classic songs and killed in the classic anime FLCL, but never really did anything for me. I've played one, but it wasn't a meh experience. Nothing magical.
Any bass with less than 21 frets.