Near the end of Stage 2 (Stadium), you will be running from rooftop to rooftop. Midway through the rooftops section there will be lightning that starts to strike. This is best unlocked when playing on Easy as you will need to use your lollipops in order to stay alive. When you see lightning strike try to walk into it to get struck!
Note: If you get killed by the lightning before getting a checkpoint then your struck counter will be reset. Make sure you have plenty of Lollipops to replenish your health so that you can get 10 strikes.