If you're in public and feel negativity, you will probably want to practice some energy clearing you can do while in the presence of others. You don't want to do anything over the top, but you do want to do something that will help you feel better.
Examples of negative energy in public -
Seeing an ex
Dealing with loads of people
Seeing someone you don't want to see
Getting negative or bad news
Feeling like you're stuck in a situation you can't get out of
Having low energy or if you're just in a bad mood