Bala sharks, I think they are UGLY. Of course my husband loves them and wants one for his tank, which I am TRYING to talk him out of. Told him if he got one, I was done maintaining his tank and he could do it his darn self!
Do shrimp count? I honestly don't know why, but they completely creep me out. *shudder* I was watching some bamboo shrimp in a tank at a LFS...the way they scuttle around... creeeeepy.
Guppies. Used to have them as a kid and they bred like crazy- I was constantly trying to find homes for all the babies it was a nightmare... I should have done the sensible thing and let the parent's eat the fry rather than using the breeder trap.
I still have nightmares where I have a guppy tank again- and the numbers increase visibly whilst I watch until they overflow the aquarium in a writhing mass of bright gaudy colours... as if it is some 80's music video.
/ yes that is my serious answer.
Goldfish arn't ugly... normal goldfish anyway- those ones with eyes that pop out of their heads are hideous though.