Nice, and since you will be in the store how about helping yourself to a nice flatscreen tv or perhaps dip your hand in the cash register?
Edit: unless you don't actually mean how your post reads?
you could class it as being a bit cheeky i suppose but not theft, if the suit is still retailable you're just extending the 35 day return policy by buying a new one that DOES fit and taking back the one that doesnt on its receipt, saying that it doesnt
