Which individual activities and
choices do you find most harmful to the environment and
why?

Some of the individual activities are overexploitation or overutilization of resources.

Explanation:

Humans influence the natural environment to large extends some times beyond repairs as their consumption and production are both ways harmful to the environment, as the industries and manufacturing sector have alone contributed to large scale pollution over the land and water sphere. Large scale exploitation of resources and overuse have resulted in depletion and mass extinctions of species and as a result, have downgraded the performance of the earth's natural ecological systems to bounce back. Use of agricultural HYV seeds have destroyed soil productivity and damaged the flow of nutrient from the soil. Also, the use of artificial pesticides and greenhouse gases have punctured the entire ozone-producing gas and thereby have created climate havoc on the earth's surface.

Ibelieve the answer would be a large-scale natural disaster