Originally Posted by cynicAAl

any used cup has probably been in contact with the passenger's mouth. If it's refilled, it's probably handed to the FA, who grabs it and touches the rim. Then they probably touch other cups (new or used) with the same hand and the spread of germs and viruses begins. I know new cups aren't sterile, and I'm far from a germaphobe, but I think a little plastic waste (which is ultimately recycled) is a small price to pay for preventing the spread of herpes or whatever.