Michael's mug that he bought for himself at Spencer Gifts with the words "World's Best Boss." printed on it. In "The Secret," Dwight places the mug in front of a temporary entry as an obstacle for a gold ball, when Michael orders him to put it back to prevent him from chipping the mug, he places it on the desk; Michael knocks it down shattering it and blaming Dwight, who then offers to pack up his belongings, Michael proceeds to tell him it's not necessary, pulling out an identical replacement. He bought one for Jim as well when he became a co-manager. It was revealed that inside the mugs was Gin. Creed takes the mug for himself when Michael leaves for Colorado.
The mug is available for purchase here: bit.ly/UQ6z9d