Stupidity seems to be incurable, doesn't it? People's stupidity for lack of understanding, for lack of study, for lack of zero proof and evidence-based facts for what they are shouting about drive us mad, don't they?
When people talk behind us for spreading falsehood about us is inconsolable, isn't it?
My advice is if you are asking me, ask that person why. Calmly and cool. Ask them for proof of what this person is making in his/her speech about, to you, is wrong and doesn't feel right or you know he/she is wrong.
If he or she will not answer your question for proof and evidence about their claims, then, present yours.
If they continue with their stupidity for lack of knowledge, it's their peril. Not yours.