Smokers as Invalid Witnesses
A person who is aware of the severe damage that is caused by smoking cigarettes, and continues to do this, transgresses the prohibition of “Take care of yourself” (Deut. 4:9) and “Now you are to take exceeding care for your selves” (Deut. 4:15).
A person who knowingly transgresses these Biblical prohibitions is prohibited from serving as a witness.
For a previous pesak of Rabbi Abergil see here.