Ad Hominem Fallacy

What is ad hominem (personal attack) fallacy? 

Ad hominem → "argument to the man."

To attack the person creating the argument, instead of the argument created by the person.

Example 1: "Of course your argument doesn't make sense! It's because you're an INFP." 

** underlined and bolded part is a personal attack made against the person's MBTI type. 

However, not a fallacy if relevant.

Example: Tannie has testified that he is 15. However, Tannie's friend said that Tannie is a compulsive liar and shouldn't be trusted. Therefore, Tannie's testimony should not be instantly taken at face value.