I had an auntie who works as a prison nurse in the US. She gets burly patients who can take a shanking without so much as a flinch, but will cry like babies once she and the doctor bring out the syringes.
^my totally unresearched and uninformed speculation would be that these are individuals who are so deprived of being in touch with their more sensitive sides by being involved in a machismo dominated culture of violence that a syringe is a freebie "out" for them to indulge in their inner softie