You can do it. Hell, you can even cram a 12" rhom in a 20g tank, but before you do, ask yourself this question: what does really matter to you? Keeping healthy fish that have enough swimming room and are comfortable in their tank, or just stuff as many fish in your tank as possible, probably making their lives miserable?
That people say they have tons of fish in their tank doesn't mean those fish are better off, or even healthy/comfortable. But it doesn't necessarily mean the opposite either, however.
Piranha are territorial and hierarchical fish: people can choose to ignore that, but that's their choice - sooner or later they'll end up posting some "Help, everything's going wrong" thread, trying to fix the mess they intentionally created.
The xx-gallons-per fish rule is indeed a guideline (but one that keeps the well-being of your fish in mind), but it's starting to become an obsolete one. Not gallonage determines how many fish can be kept in a certain tank: for example, a 50g could be a high, long, bowfront or hexagon tank, and all support a different amount of fish.
If you want an accurate suggestion of how many fish fit your tank, we need to know the dimensions (foot print equals surface area, and that's the determining factor, nothing else) - the amount of gallons is too vague to base any solid recommendations on.
mshaughnessy: retarded indeed - why should anyone bother wasting words of (well-meant) advice on people like you, if that's how you see it?