Why transfats are worse than regular fats?

Because "transfats" do not and have not occurred in nature, they are entirely artificial, a result of the factory processes. Because they are not natural, natural systems in the body have no mechanisms to process them (use them or change them) and they therefore accumulate and eventually cause illnesses.

Regular fats can be used by the body to make need chemical the body needs and "burned" as a source of energy for the body. Bodies NEED natural fats.