Plecos, too...
The one that bugs me, personally... and it probably is just me... is the sale of common plecos. I remember seeing one in the NY Aquarium which was longer than I was tall (it was latched onto the front of the display and you could stand next to it to get an idea of its length)... The thing was about 6' long! And yet, they're sold as suitable for aquariums... No one mentions that when they get big, they get aggressive and will go after anything of smaller or equal size -- in the case of slow moving Goldfish, size isn't even a factor they just get attacked. The species profile stated that the huge pleco is commonly sold for aquariums of all sizes.
So that's my gripe... *=+P