How much bodily fluid needs to get inside a persons body for them to get an STD?

So about two years ago something happened, now me and another guy were both wearing boxers and the other guy guy probably hadn’t hit puberty yet (we were both around 12) and a little bit of something may of have got inside my butt hole (I really doubt it though) (If anything did get inside it would have been just a tiny drop) is that enough bodily fluid to get an STD?