OH! Man, I hope you're ok. How the hell do you mistake a tendon for a vein? Veins are clearly a very different color from tendons. If you have dark skin or your veins aren't that visible then I can understand a bit better. Like I said, I hope you're ok and you don't have to go through something like this again. Hope this doesn't stop you from donating blood again in the future. Try asking for a more experienced nurse next time. I believe you can do that in most places.

your so vein

(joke, for any of you idiots that'll see it and immediately critique every part of this)