Hello!

I need a word from the English language that best describes this meaning:
"Someone who only takes in things or information that they see that support the agenda that they are trying to prove really exists (In a bad way)."

What I am trying to say is, someone who takes in information about a negative side of an individual and using that information against him/her to cause anger.

To put it into a more simplified and detailed version...

Person B | YOU
Person A | Maybe someone who is your friend or someone you know.

Person B has done something wrong to Person A. Person B is a kind and loving character and is loved by the majority of everyone he knows. Now, because Person B has made Person A upset, Person A wants to gather any negative information that Person B has used to make Person A angry. The information will be used as evidence against Person B to make them feel sad and angry and to cause anger between Person A and B.

I have put the scenario there for you guys to figure out what word BEST describes this situation. This may apply to things like, online arguments and jealousy.