It's common sense that when you step on someones shoes, no matter how old or new, it's a blatant sign of disrespect. If this person happens to be a sneakerhead then the situation you just got yourself into can quickly escalate into a full-blown problem.
Admittedly, everyone handles this offense differently but the only way to accurately illustrate someone stepping on your kicks is through Chappelle's Show GIFs.
You can try to, laugh it off:
Look the person square in the eyes and don't say anything, they'll get the message:
In case the offender isn't aware of what they just did, you can give them a lecture:
Or, you could make a scene:
To show you really mean business, react with an open-faced slap, and keep it moving:
If it's not a big deal, act like nothing happened:
But, some might call up their boys, explain what happened, and ask for back up:
Others might just make threats to intimidate the offender:
If the damage was bad enough, get violent and kick the person as hard as you can:
Ultimately it's probably best to let it go. They're just shoes after all, right?