ooo I love a good rant!!
I agree with the above sentiment, especially small tanks with a huge internal filter, big heater etc taking up half the tank space.
I also hate that most people make little or no effort to learn and use Latin names (and being a really picky bastard I hate it when people capitolise the species name! It is Genus species, always lowercase for the species!!!!)
I hate just about anything artificial looking in tanks (pirate ships, fluro gravel, plastic plants etc etc). Similarly I'm not relly a fan of the empty glass box look, although I prefer that to pink gravel and a sunken ship...
I hate tanks that are taller than they are wide, just looks silly and two-dimensional to me, yet they seem to be the most popular tanks.
I hate seeing tanks with a total mish-mash of fish, where no planning has gone into the stock list (like having 2-5 each of half a dozen different schooling fish in a community tank), and I'm not really a fan of mixing rift lake and new world cichlids.
I hate seeing clown loaches kept in small groups (<10) in small tanks (<6').
and the number one thing that grinds my gears....
I absolutely HATE people referring to rift lake cichlids (usually Malawi) simply as "Africans" or "Cichlids" as though no other cichlids exist!!!! Seems to happen so frequently on our local forum, "I want to start a cichlid tank, what should I put in it?" then they get all confused/pissy when you suggest angels/apistos/eartheaters/anything not from Lake Malawi/Tanganyika...