Assuming the weather is decent, you dont want to be @Disney and you have a car why not...
Head down to Laguna Beach and spend the evening watching a sunset, checking out the odd stores and having a bite to eat?
Try Medival Times for a very comical (yet strangely fun) dinner?
Go to the Irvine Spectrum or South Coast Plaza and laugh at the yuppie mall (or just see a movie after window shopping)?
Attend a sporting game at Angel stadium (cheap tickets are real cheap)?
Or better yet, catch something on tv, eat dinner and prepare for your adventure!