It needs basically a set of near perfect circumstances to allow for infection
. Therefore, a person CANNOT get HIV
from environmental surfaces, like toilet seats, manicure/barber equipment, shower stalls, drinking glasses, toothbrushes, etc etc. The virus quickly becomes inactive when it is outside of its host (the body). This is why infection from inanimate objects is impossible. This is also why mutual masturbation with exposure to a partner's gential fluids is also NOT a risk in any way.