I would say tanks that are in the 96" range are monsters. My friends think my 125s are rediculous, but I just think they are a good size. With my 125s I can easily move them around and reach in to clean them fairly easy. My standards are changing though. I purchased 6 55 gallon tanks, because I thought they were a descent size but now I feel that they are terribly small. I'm currently looking at replacing all of my 55s with 75 gallon tanks. So its all relative.
Yea, we covered this topic already. I single-handedly decided for all of MFK that 1000gal was the minimum to qualify as "monster", and it stuck. Everyone else is small-fry.
A neon tetra in a 55 is monster. Is one large tank, like Johnptc's giga tank more monster than someone with 10-20 100g tanks?
To house large fish you need large tanks, but to be monster you don't need a large tank necessarily.
Normal fish keepers over here have one average size tank, which they keep X community fish in, 90% of LFS sell tropical community fish. I have 4 tanks, all but one falls into the other 10%, and then there is the small matter of the pond, that will be finished in spring.
To me Monster = Passion for fish keeping, size doesn't come into it