It is commonly held belief among the more fundamentalist christians in the United States that atheists lack morals, are self centered and don’t care about others. The list comes in many variants and is hard to argue against, not because it is true, but because many believe it to be despite evidence to the contrary.
Or the claim that we atheist do believe in a god, and the assumption it is the particular god they are arguing for, we just deny it and burry the belief as deep as possible. Most often this is followed with some reasoning that we do this because we want to sin in some shape or form. To indulge as much as possible with no regard for the consequences.