A serious overheard threat, play it off a pissed off venting or do you do something?

Would you get involved or steer way clear if it? The details, you are traveling home on the commute train and you are pooped, you get tired of reading the paper and you slump down in your seat to rest your head and you close you eyes paper draped across your lap; and appear asleep. About 2 stops later to people board and sit across from you. They start talking (young females) at one point in the conversation you hear one say “I hate that Mr. so-and-so, he is failing me for no reason, I am not going to let him fail me in my AP class. I will fry that SOB”. Other girl, “How? Sick your dad on him? (giggle). 1st girl “Yeah…..I will just put the word out that he touches girls inappropriately and he tried to grab my tits” Second girl “sssssshh…***** what about that guy” 1st girl, “Don’t sweat it, he hasn’t moved, he is asleep”. You slyly squint a peek and see two high schoolers in cheerleading uniforms and figure they are on the way home from a game. The 1st girl is fuming because she figures this teacher is going to tank her AP class messing up her college aspirations. She ask girl 2 to corroborate her story if she floats it out there and the 2nd gal reluctantly agrees. A few stops later they off board. If you recognize the school uniform and where the girls attend do you go there with your story which you can’t prove, or say nothing in case it was some pissed off girl selling “wolf ticket”?