Ask them how they are doing or what they are doing in a boring nicety type way.
Ask them if they are looking for anything in particular.
If the answer is "No, I'm just killin' time/Just bummin'." I tell them I will let them look in peace and to let me know if they have any questions about anything. (A product of service in the store.)
If the answer is "Yes." Well, you can probably guess what is next.
As people who are "Just bummin'/killing time." walk around the store, I don't suffer insults from them. Period.
I opened, own, and operate this place by myself. Without any help from anyone else. I clean it, I maintain it, I pay the bills, and I make sure it is a safe environment.
Folks who attempt to try their hand at insulting me, my shop, my merchandise, my profession, etc, find I'm pretty tenacious at defending myself.