How does One Stop someone from Littering?
Please understand people are NEVER inherently immoral, and it's not even our duty to pass judgements on strangers by shouting or shaming.
When such a thing happens,
1) Put on a smile on your face and gently ask the person to not do it so and encourage
2) If possible, strike a conversation and ask them (him/her) to encourage other 10 folks to not litter
Let's increase the strength of our 'pride', folks!
Let's practice inclusion than using crass tools like shaming, mocking, and excluding.