Dealing with Satanist(Youth especially)

Dealing with Satanists... How do you do it? lately i've had some Satanists hang around my shop(Outside) shouting in "God doesn't' exist" and chanting "Hail Satan" when I walk by them. Some teenagers. I just tend to ignore them myself. But it's actually getting pretty annoying...Do not these teenagers have something better to do? When I was their age at this time of year, I was busy being out doing everything, now they hang out infront of my shop and do that. I want to punch them in the face(in my flesh), but I know the SECOND i do that one of them will be recording with the phone and upload to youtube "Look at what Christians are doing to us" soooooo best not. Also it's not very turn the other cheek-ish to slap them upside the head i suppose. I do however want to challenge their statements. 1. God doesn't exist. 2. Hail Satan. Ok soooooooo who is Satan then if God doesn't exist? if God doesn't Exist then Satan surely should not as well? Cos I mean Satan's only reason for being anymore is to challenge/Accuse the saints before God. And later to wage war in Heaven. So without one how can the other exist? I dunno anyone got any ideas how to approach this?