If a random man walks up to you and starts talking, bring your phone between your body and theirs, and pretend to text. This will help make them feel uncomfortable and walk away.

This has happened to me many times in my life. No one needs some weird schmuck walking up to you and making you feel uncomfortable. If you don't want to full on ignore them, then bring your phone between your body and theirs and pretend to text. They'll feel like an idiot, and they will walk away.