I just got reminded of this one:
I have one client who I do some regular maintenance for them and almost everytime I've made a change and ask them to check it b4 i put it live i get a phone call:
Client:"i can't see any of the changes"
Me: "Have you refreshed the page?"
Client: "Oh, i have to do that everytime?"
Or the other common one is
"How do i clear that cachey thingy again?"