That's not a rule, in fact the Pepsi Challenge is one of the most successful marketing campaigns ever and it mentions Coca-Cola by name. In general, market lea

That's not a rule, in fact the Pepsi Challenge is one of the most successful marketing campaigns ever and it mentions Coca-Cola by name. In general, market leaders will not reference competition to not give them credibility/free advertising, but the other way around is fair game and is often used quite effectively.