A man gets on a commuter train for the first time and sits down.

One of the regulars yells out 11. Everyone on the train laughs. Another regular yells out 4 and a moans are heard echoing in the car. Then a 47 is quietly mentioned. Giggles are heard. The new commuter asks the person next to him what is going on and is told that everyone on the train car has been coming for so long and the same jokes are told so frequently they have assigned numbers to the jokes to make it easier. The new commuter decides to give it a go and yells out 31. The train car is silent. The new commuter looks at the person next to him and asks what he did wrong and is told, “Some people can tell them and some people can’t. It is all in the delivery.” Asking for a friend… where is this subs numbering system located?