My dad would step backward onto their toes. He was a 200+ pounderAmen.
I especially hate it when you are in a queue, and the person behind you doesn't give you any space. They seem to think they will get to the front sooner by crawling up your ass or something. There are a few things you can do, such as turn around and face them, or put your arms on your hip and stand sideways, or tell them to just back off buster! But there is only so much you can do, since you don't want to lose your place in line.