Hmmm, There are a lot of fish that dont appeal to me enough that I want to keep them but there are many that I truely dislike completely.
I really dont like dyed or grossly hybrid fish (like "fancy" goldfish).
Fish I wouldnt want to keep (mainly for no specific reason):
Most live bearers (guppies, molleys, etc).
Most very large fish (I'm one of these people that mainly prefer a shoal of 20 fish to 1 big one).
Arowana - I REALLY didnt get these fish until I saw the video in CFC's massive tank building journal. After seeing it swimming around in such a big tank I suddenly saw how cool these fish actually are.
Thats about it really and there are exceptions to the above (I love discuss and Angel fish which I class as large fish).
Neon Tetras and Cardinals, you get them home, they go to the bottom, they disappear, they die.
Either there is something very wrong with your tank or your LFS sucks. I have had neon and cardinal tetras that have lived for years.