If you want some obese woman's fat grubby hands on your junk, by all means, go ahead. If I'm going to be publicly groped, they should at least be attractive enough to justify it.
If they already had a guy pointing a camera at her ass, why couldn't he just take the picture instead of risking her catching blondie tagmaster in the act?
This happened to me once with a friend, but not walking. What happened was I went to hug my friend from behind, I executed said hug. When she turned around the palm of her hand touched the tip of my dick. She knew she touched it and said "I touched your... you know... your thing" and she touched it again for a good 5 seconds.