a word that grandmothers and overly-churched individuals use in place of "god." also fun to use for the sarcastic value; it's equal to saying "I was such a huge fan of N*Sync. they rocked my socks."
grandma: "oh my gosh, you don't attend church every sunday for six hours?! you heathen!"
Lauren: "oh my gosh! what's wrong with me?!"
(as you picked up on, everything Lauren said was sarcastic.)