In TFC the medic could infect enemies with his med-pack. The enemy would slowly lose health, but also would spread the infection when bumping into others (The noobs didn't realize it, but some people also abused it for griefing). Lots of colorful dialogue there ...
Lol, yea, used to take advantage of people not knowing what it was alot, or how to cure it. 2Fort I used to conc jump up to their battlements then stand at their spawn exit spamming the medkit. Guy comes out and gets infected, may or may not kill me but runs back in to pick up health. Then stays in there to keep picking up health, infecting everyone else as they spawn. Yup, colourful conversations followed