Well, I'll be hogtied and hornswoggled!
Obviously refers to cowboys roping and throwing calfs or cows, securing the rope to the saddle horn (hornswoggled)and tying three of their legs together with the 'pigging string'.
When a woman(or gay man) invites a man to their home under the pretext of a friendly hang out, but with their subtext being, "I'm gonna fuck that guy."