I hope you can get to the point where you no longer give a crap about those people and find a way to live for yourself or someone you actually care about.
That said, spite living is still better than not living at all. I wish you a chance at a happier life.
I'd keep things semi formal in terms of what you call things (proper names rather than slang). Keeping a sense of formality, I think at least, takes a little bit of the weirdness out of discussing things with a parent.
Plus remind that it's all a natural thing and that they're welcome to ask questions without judgement. Safe sex info and that is a good idea too probably.
I guess you know what your kid can handle.
Hopefully some of this is useful to you