Heh, it's the same dance every time.

"Have you donated from this arm before?"
"Yes, always the left arm."
"This is a very narrow vein. I will call a more experienced colleague [this time a super young lady in a headscarf 💚] to do it."
(I'm happy they do check! It's just always kinda funny ... I can tell them by now that there are two veins and that it is easier to feel them than to see.)

And then they are surprised that I'm done in 5 min max. Narrow veins but good blood flow.