Fallacy of invincible ignorance
The fallacy of invincible ignorance, not to be confused with the theological concept of the same name, is probably the simplest logical fallacy. It consists of simply maintaining one's position after it has been disproved. As an example, homosexual activists maintain their position on same-sex marriage even after having been shown the harms that it inflicts on society. On the Internet, the fallacy is commonly known as "La la la, I can't hear you."