These days we could do with some reasonable definitions of flirtation, consensual erotic activity, and consensual sex. All these are things that happen between two people. (Sorry, I'll only be talking about pairs here.) Flirtation happens between pairs who are interested in erotic intimacy, as well as between pairs only one of whom is interested in erotic intimacy while the other just feels like flirting. Consensual erotic activity can include not only flirting, but touching implemented by one person and not rejected by the other. A pass can be accepted or deflected. If it's not deflected, it's accepted. Hopefully it's enjoyed, but acceptance doesn't mean enjoyment.
Sex occurs between people who both want to have sex, as well as between pairs of whom one wants to have sex and the other doesn't feel like it but does it anyway, or is ambivalent but has decided to do it anyway, or is enthusiastic about it at the time although s/he will be disgusted by it later. (Shakespeare wrote a sonnet about that. Such sex is "past reason hunted," and then "past reason hated.") Consensual sex also happens (a lot) when one person is agreeing to it only because s/he is
