I, once, locked the keys in my car, with the car running and the headlights on, when I went to pick up my date. Instead of going out immediately, we had to wait until my friend could drive to my house, grab my spare car key and drive it to where she lived which was 20 minutes outside of town. (true story) I wish I knew about this technique as it could've made me look like a handyman in her eyes and save me the embarrassment.

Remember to only do this to your car, please.