Disgusting experience in Kaifiyat Express AC coach, what should I have done?

Recently i was travelling in kaifiyat express, AC COACH, i fucking went to use the bathroom and guess what? I found someone's cum on the sink, someone who went in just before me busted a nut in there, and i am a teenager and i couldn't tell my parents about it, i had the courage and I confronted the person who got in before me, and he was reluctant and ignoring me, acting as if he couldn't hear me, this behaviour made clear that he did this deed. Honestly wtf are people even doing in life, and as a 16yo, what action could i have taken in a situation like this?