Question: How do you approach somebody with bad underarm odor in a public trans?

You Know what, it's quite rude if you say to them that they have a bad odor, but it's better to inform them because some of them don't notice that. It's a great tip for them actually, because it's a shame for that person and in that way he will know about it and they know what to do next time. So approach him and tell him that he has that in a nice way, in this part it depends on the person how to say it=)

I wont approach him/her as dont want to disappoint and offend a person. I'll just look for a better place to take a deep breath and take away from pollution. If that one is really aware of hygiene, he shouldnt have been that desperate to disclose his refuse.

I never tell strangers about their odor unless they ask me. I would just bear it until it's time for me to get off the bus or trolley, or whatever. I also believe it's rude to approach someone you don't know and talk to them about their odor. It's very possible that the person can't do anything about it because they're homeless and can't bathe or change their clothes. Some people just have a problem with odor no matter what they do because of a medical condition. So, I would probably either find another spot to stand or sit, or I would just tolerate it until I or they leave.