I accidentally saw my sisters best friend topless. Do I apologize?

I think you should, if you do it right maybe you get lucky 😉

if she is hot . you should've took a picture of her or asked her if you can motorboat her

as a girl i don't think so but try to feel her emotion or reaction over it after you saw her , once i was caught completely naked by a friend of my elder brother and that ended with a thrilling exp of sexual relation between us

Does she know you saw her?

What for?

Nope

was it your fault? why raise the issue?

It was not a "hit or run" case, so you are safe.

No need to apologize.

no