During our initial Engineering days we used to go to "Honu/Manoj" dhaba nearby our hostel for the evening snacks. For the initial 2 months all the 1st semester guys had to wear complete formal all the time. So we used to visit the dhaba with our formals. We noticed that most of the seniors never used to pay the bill, instead they would simply say "kikhi thobo" ie. "please write it down"
After few days we also started to say "Dada likhi thobo" ie "Bro, please write it down". Sometimes when friends used to visit we usually used to say "Mur naamot likhi thobo" ie. "please write it down in my name".
It all started that time and some how it become a never ending process. Only difference is now a days we don't have to tell any one "Bro, please write it down".. everything is automated.