Grammar police here: plural of 'penis' is 'penises', no room for two eses in penises! (Or if the word is Latin, then it would be 'penisi'?)
I think the word would be “peni”.
Shouldn’t the stagehand be wearing latex gloves while holding the, um, patient, still in order to make the injection? If so, it would be more difficult, although certainly not impossible, to inject oneself accidentally. And, if he did, wouldn’t such an accident be his own fault or is he claiming that he was subjected to unsafe working conditions?