We all hear the cry (from our teenagers, if not many others), "But everybody's doing it!" John Calvin called it "The Appeal to 'Custom' against Truth" in his Prefatory Address to King Francis when he wrote his Institutes:

"Even though the whole world may conspire in the same wickedness, he has taught us by experience what is the end of those who sin with the multitude. This he did when he destroyed all mankind by the Flood, but kept Noah with his little family; and Noah by his faith, the faith of one man, condemned the whole world (Gen. 7:1; Heb. 11:7). To sum up, evil custom is nothing but a kind of public pestilence in which men do not perish the less though they fall with the multitude."