I hoped to sign the birthday card our team bought for Coach, but I couldn't find a spot to sign my name because someone went all John Hancock on it and signed his name across the whole card.

2 answers

What is the meaning of the phrase "went all John Hancock on it"?

The phrase "went all John Hancock on it" means to sign one's name in a very large and noticeable way, similar to the way John Hancock famously signed the Declaration of Independence.
Lol, probably get a new card XD.