Collecting used glasses, cans etc in the cabin-
I pick up a tray in each hand, a glass of juice is still on the table. I'm about to tell the lady that I'll come back in just a second for the juice.
Lady: "Hey hey you forgot the juice"
Me: "Madam I will be back in a moment to take your glass."
I take the trays to to galley and come back (now with free hands) to take the glass. As I'm leaning over to pick up the glass:
Lady: (angrily) "Hey you lazy, you need to pick up the juice"
Me: (In my head): Give me a freaking chance and maybe I WILL pick up the juice!!
Seriously people, give your flight attendant a chance to do something before you berate him/her for not doing it. Odds are, they know what you're about to ask and are going to do it. Telling them off for not doing it before you've even waited to see if they're going to do it will just make them annoyed with you, and slower to come back next time. Free tip for you... :P