It is the 1066 return of Halley's Comet that is portrayed on the Bayeux Tapestry foreshadowing the defeat of King Harold by the Normans. Aztec emperor Montezuma II saw the bright comet of 1519 and thought it portended the arrival of the god Quetzalcoatl with a white beard. Who came instead was Spanish conquistador Cortes, also of white beard, and that was the end of Montezuma and the Aztecs. In medieval woodcuts comets were illustrated as being or containing swords and daggers. There's lots of other examples.
Bad things happen all the time.
Comets get blamed for whatever bad happens when they are around. Perhaps the previous comet. Astronomers understand very well the forces that govern the motions of comets and the other bodies in the solar system. The greatest force is between the body its self and the sun. However the gravitational force between that body and all the others in the solar system also affect the orbit a bit.