Okay, a first-hand account:
A neighbor who helped build Grant's log house, John Parke, related that, "It used to be the custom in those days for a host to pour the liquor in his guest's cup, and keep on pouring till the guest would say 'when.' Old man Dent was pouring for Grant once, and Grant kept on watching the liquor raise in the glass without saying anything. The tumbler was getting full and Dent was getting mad. 'Dammit, Grant, will you never say "when"?' exclaimed the old man, and everybody laughed, for we all liked our liquor in those days, but Grant most of all."
By the way, those little explanations that Grant would get drunk on just a drink or two are, almost undoubtedly, mere excuses for his alcoholism.