The background for this story is of course that Peter denied the Lord on Good Friday.

Saints Patrick and Peter were at Heaven's gate and looking down on the world. Patrick said "Look Peter it's my holiday and my people are joyous." Patrick said "I think I'll join them". Peter wasn't sure this was a good thing for a Saint but agreed.

The next day there was Saint Patrick hung over very disorganized and gennerally run down. St Peter walked up and full of indignation "Look at you Patrick you are a disgraceful mess, what could be worst behavior for a Saint?" Patrick just looked up and said "Cock-a-doodle-do Peter.