The verbal war over the Goods and Services Tax (GST) continued between the BJP and the Congress on Friday, with Finance Minister Arun Jaitley calling Congress Vice President Rahul Gandhi's idea of a single GST rate a "grand stupid idea"."What Rahul Gandhi suggested was single GST rate of 18 per cent. This is different from suggesting a cap of 18 per cent. This was the grand stupid idea. Can a Hawai chappal (slipper) and a BMW car be taxed at the same rate?" Jaitley tweeted.He was apparently responding to senior Congress leader and former Finance Minister P. Chidambaram's criticism of Prime Minister Narendra Modi.Chidambaram had on Thursday said if it was a "Grand Stupid Thought" -- as Modi had termed it -- to argue for a cap of the tax rate at 18 per cent, then Chief Economic Advisor (CEA) Arvind Subramanian and many other economists were stupid."If it is grand stupid thought to argue for a cap of the tax rate at 18 per cent, then CEA Arvind Subramanian and many other economists are stupid. Is that what the PM is saying?" Chidambaram had tweeted.He was referring to the Prime Minister's speech at a rally in Morbi (Gujarat) where Modi said: "It is natural for those who have looted all their lives to remember dacoits. Under their ‘Grand Stupid Thoughts' they want basic necessities of the poor to be taxed at 18 per cent. At the same time, they want cigarettes and alcohol to be cheaper. What logic is this?"