Can I say no to letting student peers practice poking on me? If not, advice to handle it?

I hate being poked! Shots, blood draws, anything! Its not the pain. Its the thought of exploding a ballon or blowing air into a ballon to explode that disturbs me. I have been poked 2x on each arm for a blood draw (that failed). I have to look away, and I normally vent/rant/yap to distract my mind.

Can I say no? I know socially might face some judgment from the professor, and critical peers, but i don't want to be the student who had a bad experience of being poked.