What to do when you see public exhibitionism?

Tonight (around 10.30pm), I took my friend to the medical store near medical college to get some medicine. While I was waiting by my scooter, I noticed this old man sleeping on the doorstep of a building a little farther away. But then I saw that every time a woman walked by, he’d lift his mundu and start fondling himself. It was so disgusting. He’s really old, and even though some people saw what was happening, they just walked past like nothing was wrong. I've had my fair share of people flashing at me, and I’ve always spoken up, but this time it was an old man. He seemed like he was sleeping, but not really every time a woman passed by, he'd lift his mundu and do stuff then pretend to be asleep. Man, what can you even do in situations like this? Just ignore it and act like nothing happened? https://preview.redd.it/amjoqxq8fn8e1.jpg?width=960&format=pjpg&auto=webp&s=9ad74090ef3dd7c7a944d959d8c84d97150f0a2e