I got one of those little t-shirts today. I thought it was a cute joke, nothing serious, everyone's just having some fun with each other. I don't think anyone wants to knock the other dude out of business, and I'm sure both stores can be run successfully without biting each other. Goodfoot's been dealing with Da Zone, Uptown, Nike Stores, Footlockers, etc since it opened and it's done nothing but flourish (same for LS in Van), one more store doesn't have to change anything.
And I don't think anyone at LS is getting bent out of shape by the shirt, they've been stickering/postering the neighbourhood for months and they chose to open around the corner from Goodfoot in the first place.