I hate needle scenes in movies or television, specifically addicts injecting heroin. It just makes me cringe.
I've got to say - me too. Can't watch it on TV. Real life isn't a problem, I routinely have intravenous stuff done, will watch that no troubles. I've had a skin slice taken from the under side of my upper eyelid, man leaning towards your eye with a scalpel is an unpleasant experience, but I made it.
Needles on TV though, makes me squeamish.
My only (discovered so far) real life squeam-inducer is kidneys. Something about them, not sure what it is.