McDonalds story alert. I made a $2 tip at McD's just once. I told the manager about it and he said the actual policy is that you put tips in the register. I couldn't believe it so I said "Really?"
And he's like "The reason is that your till will usually come out a little short every shift, because you make mistakes but mistakes made in the customers favor they won't tell you. So any tips help balance that out."
I kept it anyway, screw that.
If you guys really want to help someone out, tip at the fast food places, they work faster and harder than regular restaurants and they get nothing for tips, while taking more disrespect.