It's "bad language," the kind of bag language called "vulgarity." It means the person had many really terrifying experiences in life. "Puckering" is best explained by imagining someone whistling with their mouths. They narrow their lips to form a small opening. The lips become wrinkled. This is called "puckering the lips." When someone is very frightened, they tighten their buttocks and something similar happens down there. "Ass" is a rude word for the anus.

Its funny. 'Ass pucker' probably means 'scary'. You 'pucker' your lips when you eat a lemon. Think of that face, related to your ass, and you have an idea what it means.

lol, I have read and listening it on a movie called A Perfect Getaway (A Trilha).

Honestly have never heard it. And I know most slang, even dirty slang lol