You want to put a fish that gets up to a foot long (and they easily get that big, and they grow pretty fast) in a tank that is 25% of the size that it should be, with arguably one of the most aggressive fish available to us in the trade (which is also not a good choice for a 55 gallon tank) and you're going to get all upset when we tell you its a bad idea?
Obviously you didn't really care what we thought, or you thought that we would coddle you and say its a good idea.
You're next thread will probably be 'why is my tank covered in algae' because the fish you have now are already past the safe stocking limits for a 55 gallon tank, and you're going to add a very big, very hungry puffer to the mix (because we know that despite what we tell you here, you'll bring one home anyway based on your response to those that burst your bubble)