Confirmation bias is the tendency to selectively search for and interpret information in a way that confirms with one's pre-existing beliefs or hypotheses. In other words, you interpret new information in a way so that it becomes compatible with your existing beliefs, and if it can't be interpreted, you either choose to ignore it or call it an exception.
Believing that if "everybody" or "many" believes it, it must be true. This is a fallacious argument that concludes that the proposition is true because many people believe it.
This fallacy is also known by other names: appeal to the masses, appeal to belief, appeal to the majority, appeal to democracy, appeal to popularity, argument by consensus, consensus fallacy, authority of the many, and bandwagon fallacy
Poisoning the well may be thought of as an Ad Hominem fallacy in advance. If poison is dumped into your well, you don't drink from it. Similarly if someone poisons your mind about X, by telling you something unfavorable about B, you may be inclined to reject anything that X says to you.
Hasty generalization is one of the most common logical fallacies we encounter at work, study and home. Many racial prejudices we carry have their roots in hasty generalizations subsequently strengthened and perpetuated by a confirmation bias.
In Latin "Ad Hominem" means "against the man" or "against the person."
A theory is discarded not because of any evidence against it or lack of evidence for it, but because of the person who argues for it. is rejected on the basis of some irrelevant fact about the person , making the claim or argument.