Hmm, I wouldn't take the polite approach. I think, it may seem too personal and the person may be more offended/embarassed!

I think, best way is, straight out, jokingly, say it, that he is stinking! I won't give an example, but I guess you know what I mean. Do it in a non-serious/joking way, the message will get through to him and due to its humerous nature - no one really is going to take it personally.

if is someone you dont know then probably would be best to not tell them and move away as soon as possible (it would be rather awkward for a stranger to tell them that they had bad b.o.) if is someone like a family member or close friend then you should tell them quietly so that you dont announce it to everyone else around them and embarass them, and if you have deodorant with you for them to use that is even better

The Prophet (PBUH) said that ‘cleanliness if part of faith’. So we must take care to be well-groomed, keeping our bodies and clothing clean, especially at times of worship. Underpants, panties and socks should be changed daily in order to avoid unpleasant odours. It is permissible to remove the hair under the armpits.

yeh like everyones mentioned sis just put it to him nicely or jus say indirectly, give a example of imaginary persn lol.thats wt i would do just 2 not hurt his feelings.

It is sunnat, not fardh. Harmful bacteria tend to settle on pubic and armpit air, hence, it is good to shave these areas. As for circumcision, it prevents a certain type of cancer in that area.