Okay, it turns out I was mistaken. The scene at the end of Secret Six #4 was entirely consensual. But it was written to make the reader infer that it wasn't, so I'm not going to apologise for it. But then it also depends entirely on Knockout being either very ignorant, very stupid, or a bad liar.
It is claimed that Knockout has sex with Deadshot because she doesn't realise that sex is assumed to be exclusive when you are in a relationship with someone, because it wasn't that way back on Apokolips. I don't know how long Knockout is supposed to have been on Earth post-IC but she's been appearing in comics since 1994. She seems well acclimated to Earth culture but has somehow failed to notice the most overwhelmingly popular image of romantic relationships that pervades that culture.
But then in pre-IC comics Knockout is seen as something of a sexual predator, and even has a similar scene when Superboy catches her seducing Victor Volcanum.
So if Knockout is the same person she was pre-IC, then she's a big fat liar and sexually manipulative, or she is new retconned Knockout, so fresh off the Boom Tube from Apokolips that she hasn't spotted that people in stable relationships screwing around is the plot of half the dramas available in any medium. Possibly three quarters.
Which leads me to wonder what anti-heroes do in their spare time if they never crack open a novel, go to a movie, catch any daytime TV, or ever have a conversation that might include any references to relationships.