I feel I have to five star this because I totally did this as a 13-year-old. It[s amazing how worked up you can get people with harmless shit like this.
To me their posture might also suggest that they're about to dash out into the road. I don't think the people who stopped did so because they were worried about the invisible rope.
I'm not sure how this was really any better than using actual rope.
I mean, people still stop, they still get pissed off, you still mime being dragged... It's really only funny if you don't get out of the way and let them try driving through.