Anytime I've had blood taken I do the same. I've only ever heard "oh wow your veins are teeny!" or "wow, you were right, your veins do NOT like to get poked!" or something like that. They've never given me attitude or been snarky.

I'm sure my usual "oh WOW you made that look so easy and painless, much better than that one horrible time, thank you so much!" doesn't hurt either. My mom's a retired nurse, and I've learned throughout the years that it doesn't hurt to lay on the sweetness real thick.