2 Boys Claimed to have Discussed Sex to a Young Girl in My Presence so do I take a Massive Shit on Them or Do I Let it Go?

I was talking to one of my closest friends with her best friend in present. I noticed the two boys talking to her best friend and she claimed (and I am sure about it) they asked her about sex. She was uncomfortable hence she was trying to change the subject. I was really angry and do not know if I should take a massive shit on them or just let it go.