Believed to come from the English punch and Judy show that was popular at all seaside resorts. The character Punch was a proud fellow who would never admit to being wrong. This puppet character was in fact a bully with total disrespect for the law and family values. He often threw the baby out of the pram. See any listing for punch & Judy or Punch & Judy show.
The expression Proud as Punch was originally a derogatory term but slowly was reduced to expressing how someone was feeling.
1, Little Johnny was as Proud as Punch that he won the race.
2, Tom came in tonight as proud as punch that Mary agreed to be his wife.