Verbal irony is when someone says the opposite of what they really mean. This happens all the time in high school, as I'm sure you're aware. For example: Scott: "Hey, Allison, do you want to go out with me on Friday?" Allison: "Oh, sure, Scott. I can't think of anything I'd rather do." (Makes vomit motion with finger in mouth.)
Here, Allison displays verbal irony when she tells Scott she'd love to date him. Her words say one thing, but her actions say another. Also, if you could hear the sarcastic tone in her voice, you'd hear that she doesn't really mean what she says. Scott will have to keep on lookin' if he wants a date for this Friday.