people will believe anything others whisper in their ear.
I personally wouldn't waste my time with them. they are in a state of denial, and no matter what you show them, they will think its a lie and that it just makes more sense to not believe.
but, lets do talk about the flag.
if you look at this pic, you'll see its guided by a bar on the top. its basically holding the flag out straight.
http://solarsystem.nasa.gov/multimedia/gallery/Moon_Flag.jpg
it looks likes it flapping in the still picture, but its not. thats just the way it settled.
also, the flag moves or "flaps", each time a naut touches the flag or pole, this is because the touches are sending vibrations through to the flag again this is not wind.
http://www.youtube.com/watch?v=ymwE1sNm82Y&feature=related
the video is 3 minutes long. you can see for about 2 and a half minutes that the flag doesn't even move a millimeter.
mythbusters help explain
http://www.youtube.com/watch?v=hMBCfuKs9i8
and this guy has a lot to say, excuse his nerdyness, but he DOES have some good points. worth a watch
http://www.youtube.com/results?search_type=&search_query=bogosity+moon
also, if anyone claims they are finding multiple pictures of different flags, just remind them we went to the moon 6 times total with 6 different flags