Grammar Patrol on the case of a common violation/felony!
Hi, you must have grown up in NATO.
Hi, you must of grown up in the Soviet Union.
As you can see, the boldened letters will show you your error.
It's Should "have", hence the contraption "Should've". Should "of" is a common and understandable mistake, given that in everyday speech we hardly make the effort to put in the "ha" of the word.