Let's review the major points so far.
Cells have surface antigens.
The plasma contains antibodies against the cell surface antigens that are not present on the cells - they are perceived as foreign to the body and will be attacked.
If you give cells whose surface antigens can be attacked by the recipient's antibodies, there will be a bad transfusion reaction and the donated cells will be killed.
Someone like person 5, whose cells don't have cell surface antigens, can donate cells to anybody without having them attacked by the recipient's antibodies. This person is a Universal Donor.
Someone whose cells have lots of different cell surface antigens will be able to accept cells from many other people, and will be a Universal Recipient.
Now, let's look at real life. Your RBCs don't really have red, green, and purple cell surface antigens!