Why thank you AWM
That is one of my pet peeves. My kids, while I was trying to teach them manners, would hold the door open for a whole stream of people, and NO ONE would say "Thank You"... They would get these hurt little expressions on their faces. I mean, really, how long does it take to say thanks to a child and make their day?
SOOOOO...me being the ah hem... wonderful

.... mom that I am, would stand on the other side of the door, and say "You're Welcome" really loudly after they went through, and then tell my sons...again...REALLY LOUDLY... how "nice it was for them to have the manners to hold the door open, even for people with no manners"... We got a few sorrys, but most people were just oblivious.
Now, then just say your welcome to the people themselves