No, this is not about sex. lol
When someone says something that maybe they shouldn't have and the person they said it to is pissed or hurt, the one who said it uses the excuse that it just slipped out and therefore they didn't mean it, and the one they said it to accepts that reason.
I think that's wrong. I think it slipped out because that's what they most wanted to say. It's what was uppermost on their mind.