I'm really sorry about your experience working at Starbucks and how overwhelmed you were. Since I don't work at Target anymore and I have no interest in visiting my old store, I'm not really sure what the Stanley Cup is. However, if an item wasn't on the sales-floor for more than 15 minutes so that guests had an opportunity to buy it before team members, team members are not allowed to buy that particular item.
It was in the handbook, which is why no one in leadership had an obligation to tell you that the rule exists.