I exchanged a 4 pack of boxers at walmart for a 5 pack.
Why cheat the store?
I wanted to find out what it felt like to get more then I bargained for
While it doesn't really hurt Walmart's pocketbook, I think things like this could come back to bite you if you are caught. Lying and being devious is just poor character.
I think I'll try it again.
I have to advise against that, for several reasons.  You could be caught and possibly prosecuted for this theft.  Furthermore, the company might blame employees for the missing inventory, and you don't want to be responsible for that.