I once had a coworker with bad BO. Very unpleasant to work with this person in an enclosed space and said person probably thought there was something wrong with me, as I became a mouth breather in self-defence. Ick.
How does one tactfully let another know that they need to shower/wash their clothes more often? I didn't know how, so I dumped it on our supervisor to deal with. Unfortunately, the situation didn't improve a whole lot even after said coworker got "the talk". I'm glad I don't work with that person anymore - now it's someone else's problem.