Using somebody else's shaver can be really dangerous if the person is HIV positive. Infact used shavers and blades are one of the biggest contributors to the spread of HIV. This is because cutting skin and breaking pimples is common while shaving. Even if a small tiny particle of the blood of a HIV positive gets on to the shaver, it can harm all the people that use it.
You should not use someone Else's shaver. HIV can be transferred easily through blood to blood contact. If there is blood on the razor and you cut yourself it can be transferred that way. I am a nurse and have been a HIV counselor.