"Yep," John replied, nonchalantly. "They were calling my name, I couldn't resist!"
"Oh, for goodness sake! You know I was saving those for later," Sarah exclaimed, her voice rising an octave. "Now I'm going to have to go to the store!"
"Well, hey, maybe they'll have a new flavor," John offered, trying to lighten the mood.
"New flavor? That doesn't solve the problem!" Sarah retorted, throwing her hands up in the air.
"Okay, okay, I'll go with you. We'll get some new cookies," John said, raising his hands in surrender. "And I'll even help you bake a batch this weekend!"
"See? That's the spirit," Sarah said, a small smile creeping onto her face. "Now, let's go get some more cookies."
Interjection: "Oh, for goodness sake!" is the interjection in this example. It expresses Sarah's strong feeling of annoyance.