Pfft, yeah that is definitely some shit Medic would do. Maybe first time it's a prop, second time it's real but the person thinks it's a prop again (but Medic still intentionally infected himself). Then the third time he's genuinely panicking because it's doing some fucked up shit to his body, he makes himself throw up and it's insanely long and covered in blood and mucus and he's sobbing throughout and after, nearly passes out. Other person still thinks it's just a prop and tells him the bit is getting old now and it's not really funny anymore. Doesn't listen when Medic insists it's not a joke and he didn't mean for it to happen. Also very CMedic coded, at least how I see him.