Can I be considered prior art? Because I did that very thing as a kid over twenty years ago. In fact, I would say the method in question was common knowledge on the playground. Parents didn't like it because if the kid next to you did it then you stood the chance of bumping into each other unless you could get a matching rhythm going.
I also "discovered" that if you use your feet to twist the ropes around each other as you sit in the swing you eventually can cause a spinning motion in the opposite direction by lifting your feet from ground. Is there a patent for that? Did I miss my chance?
EDIT: oh wait, it seems the patent was either not granted or lapsed due to non-payment. I guess I don't have precedent for my twisting swing patent idea after all. Feel free to try it with my blessing.
Longer answer: yes, but only if the one single examiner handling this patent at the time had known of you, known how to contact you, and been able to obtain any information from you (and mind you, he/she likely could not have told you why he/she wanted the information).
The other problem is that while you did this over twenty years ago along with the others on the playground, where did any one of you publish anything describing your alternate swing method? Because to make a rejection stick, the patent examiner has to find some publication by you or one of your playground mates from twenty years ago disclosing to the public your new swinging method. This is because the position of the courts is that an applicant deserves a patent __unless__ the us patent office can prove otherwise (and "prove" pretty much means "prove to the level of a civil trial in court").
If the system were reversed, i.e. that applicant did not deserve a patent unless they (the applicant) could prove it was sufficiently new to deserve a patent, there would be far less of these "swinging on a swing" type patents.
When you are forced to spend 30+ minutes/day 120+days/year over the course of 8+years around a set of limited devices you tend to think of a lot of interesting ways to use them because otherwise it can get boring fast.
I wasn't forced to play with a swing, but there were a limited number of objects and we had to spend the time in the playground area during recess/lunch and couldn't leave school grounds. This was a suburban public elementary school in San Jose about 20 years ago.