A phrase added by someone who is incredulous to what is being said, either an exaggerated report or a vision. Very much akin to "and then you woke up," as in "you woke up from the dream you were having and realized, 'oh, yeah, that was just a dream.'"
Coordinator: Yah, and I'm going to make sure there are 150 people at the cookies and ice cream party, that way we'll make $500 easy.
Coordinator's helper: Yeah, and then Jesus came back!
Seminarian: Sure I helped Jim Wallis write that book "God and Politics."
Professor: Yeah, and then Jesus came back!