Uh, Yuck!
Are you the type of person to empty out your fries on a tray and eat them at a fast food place?  You may not want to do that.
Flying-A Germy World Up in the Sky
When you fly do you ask for a blanket or a pillow?  Do you use the restroom on the plane?  Do you read the SkyMall?  This might make you think twice or at least pack a bottle of hand sanitizer (1 0z or less of course) in your carry-on.