Old joke

This young lad is sent to prison, and he is put in a cell with an old lag who has been there donkeys years.
The old lag says “Stick with me son I’ll show you the ropes”
They go to the recreation period and sit around a big table with all the other prisoners. One prisoner says “12” and all the rest collapse laughing. Another says “31” and again all the rest collapse laughing. This goes on for ages.
Back in the cell the young lad asks “What was all that about? Why are numbers so funny?”
The old lag explains “It isn’t numbers. They are jokes. There are 37 jokes and we all know all of them - so to save time we just gave them numbers”
“Can I tell one of them? asks the young lad
“No problem” says the old lag “Any number between 1 & 37”
Next evening at recreation the jokes are flowing and the young lad chips in with “22”. Nothing - no laughs, not even a smile.
Back in the cell he asks “Is 22 a bad joke?”
The old lag explains “No Son. It isn’t the joke - it’s the way you tell it”