I stopped donating blood about 15 years ago. I have O negative blood (universal donor), and also CMV negative (can't remember what that was, but it meant my blood was safe for newborns)>
There was the time when another donor had just been told he could leave. He stood up and his vein opened up and blood started gushing everywhere. Okay, but things happen.
But the last time I went, I am lying down, the nurse is digging in my arm (and I mean digging - it hurt! Then she abruptly said, "Yeah, well, that didn't work," in a fairly loud voice and walked away. Since she had spoke loudly and was looking at the other side of the room, I wasn't sure who she was speaking to and what didn't work. After a few minutes, a different nurse came over. It seems that the first nurse couldn't hit the vein. Second nurse pulls out the needle and announces, "You missed the vein and got a chunk of tissue stuck in it!" as she waved it around. She looks down at me and says, "Should we try again, or do you want to leave?"
I was out of there, and I have never gone there again.