Agree with all the others, WAY out of line. I blame the hosts too in a way since the whole thing seems sort of out of kilter since they didn't bother to inform you what kind of party it was. It would be different if every party was a swinging party, but when every other party you've been invited to there has been vanilla, then obviously that's what you are going to expect this time too unless told otherwise, which they evidently couldn't be bothered to do. Some people are like that though, just assuming everyone will take things in stride and be ok with it no matter what. Those type of people make me nervous...
Our house party experience is very limited, so no similar experiences there, but Mrs. cplnuswing has had a couple of times at swing clubs where an invitation from her to a single guy to dance obviously meant she was just dying to have his finger in her pussy about 20 seconds after stepping on the dance floor. So, moral of story is venue doesn't matter when it comes to dickish behavior.
When it's happened, I just heard about it after the fact. She would just push his hand away and tell him no, and they've listened, so she would just pull back some to put some space between them and go ahead and finish the dance. Brilliant move there dude...let's see, you went from some big ole titties pressed up against you while a pretty woman was dancing with you and chatting you up, and that might have led to an invitation to come back and sit at our table with us, which might have led to much more than that. Instead, you got an awkward junior high dance and then got to go back to the bar to sit there with the other single males the rest of the night (at this club single males are restricted to the bar area unless invited by and accompanied by a couple to go anywhere else in the club).