A statement of utter disbelief expressed when one finds themselves in the worst case scenario. Can be announced slowly and clearly to express disgust and hopelessness, or loud and fast to alert someone of an imminent disaster that will most likely end in catastrophe.
When Ted realized the car was running out of gas, he pulled to the side of the road and got out of the car. He muttered "JesusFuckingChrist" when he saw that he just drove over nails and now had two flat tires.
Just before the fireball, Ted screamed "JESUSFUCKINGCHRIST!" as he saw Fred trying to light a cigarette while pumping gas.