Tricked! Brazenly nailed on the public beach!

I finally wanted to relax a bit and was on vacation with a friend. She creamed my back and then went to the hotel. Then a guy approaches me and asks me if this is supposed to be an offer? I really didn't know what he wanted from me until he told me that "fuck" was written on my back. As soon as I could say something, he groped me and pushed his finger into my cunt and fucked me right on the beach. We had enough spectators and one guy watched us and almost cumed at me. Uff that was bold, but what should I have done? Would you have insisted on my offer too?