I had a phlebotomist tell me I should always ask for butterflies.
Took me a while to learn the best way for me to ask, and now I each time I have a draw I run down my spiel:
"My veins are very thin and rolly, but they do work. I've been told I should always ask for a pediatric needle, but use whatever you like. My veins do work, really."
Since developing my spiel, I always get a butterfly needle. Before, when I would ask specifically, half the time they'd ignore me and start with a regular needle and make a horrible mess (I tried to pass out more than once) and then have to use a pediatric anyway.
"If Americans want to live the American Dream, they should go to Denmark." - Richard Wilkinson