I gave someone the stink eye at a store.
Did anyone else in the room catch what you did?
Yes, one of my friends was with me at that time.
You should not be rude to people in public. Someone might take it the wrong way and be very upset, or they might think you are a crazy person.
No problem. Should I glare at them too?
No, you definitely should not be glaring at people who reacted badly to the first instance of you giving dirty looks.  The best thing to do is to avoid giving the stink eye to anyone in public, because they are just people going about their business.  They don't deserve this kind of treatment from you, or from anyone.