There is provided a method of making a heat treated (HT) coated article to be used in shower door applications, window applications, or any other suitable applications where transparent coated articles are desired. For example, certain embodiments of this invention relate to a method of making a coated article including a step of heat treating a glass substrate coated with at least a layer of or including diamond-like carbon (DLC) and an overlying protective film thereon. In certain example embodiments, the protective film may be of or include both (a) an oxygen blocking or barrier layer, and (b) a release layer. Following and/or during heat treatment (e.g., thermal tempering, or the like) the protective film may be removed. Other embodiments of this invention relate to the pre-HT coated article, or the post-HT coated article.