You'll hear it all the time when you're eating a crispy snack, unless you don't happen to have a skull. It's a very satisfying sound in this case. But hearing "crunch" is a bad thing if you're eating cheese or tofu. Just to let you know, you shouldn't be eating either while cruising down the freeway or BASE jumping. But if you're at home, check your teeth or check if a meteorite has crashed through the ceiling. If you're eating a King Cake at Mardi Gras time, the sound is good news AND bad news. It means you got the plastic baby stuck in the cake and you need to go to the emergency room if you swallowed.
A common crunch is heard when you're driving, often preceded by a loud screech. It is best heard off in the distance instead of right next to you unless you have the stereo cranked up. If it is heard right next to you, you are required to walk around your car to check for damage while making a face, ignoring the other car, the tree, whatever. Be sure to stop your car before you do this. If you are upside down at this point, you're already stopped and you are not required to walk around your car upside down.