The London Underground conveniently closes at night from around 0030 to 0500 (because obviously everyone's asleep then).

Catching a 'tube of shame' is when one catches one of the early morning services home after a particularly massive night out, or worse one-night-stand.

The 'shame' is normally attributed to a combination of a comedown/hang-over you have and the reflection time you have on the train as you piece together what actually happened the previous night and how to explain it to friends.

When you eat dirt for the first time and leave your family to build a shack in the woods