Go and talk just listen and at the end speak to him 
 why do you want do such a things in front of every one ?
won't you realize that if you will do like every one will see as dog ?that is litering around? 
ask him related to that  and make him feel shame and create a hate rate in hi, to stop continuous in work not any more.
every one can do this
1. Educate all your family and friends about littering and how bad it is. If you want to take it even a step further, you can become a guest speaker about the impact littering has on the environment.
2. Form a community service group
. You can help with picking up litter. If you want, you can also erase graffiti and plant trees.
Every time you see someone you know littering, ask them politely if they would use a trash can because everyone likes a clean environment

Do not expect to be able to do everything. It is impossible. Do what you can