First build up your story like say you were going to work/school/highschool/college/work etc and with that say that you bought the coffee and you were in a rush for work or your highschool etc...
And after that tell them when you took a sip of your coffee or any other beverage from starbucks that it had an odd taste or it tasted funny.
They will ask you for your receipt tell them that you threw it away or you didnt take the receipt.
They'll assist you and after that they will send you a starbucks giftcard in your mail 7 - 14 Business days.
*Make sure to give them your exact name and mailing address*