his zipper is open

Me being the blunt person that I am, I would just tell him "Your zipper is down." but I wouldn't do it in front of other people so he wouldn't think I was being rude of trying to be funny. If there were people around I would try to make eye contact and then mouth it "zip your zipper". I would want someone to tell me rather than have me walk around showing off all the business so I would just tell him.

If you just walk up to him, where no one else can hear, and just say, 'Excuse me, I just thought you might want to know, your zipper is undone", it would be a lot less embarrassing than to suddenly realize that his fly is open.

I would tell him but not outloud. I would give him a piece of paper and tell him that his zipper is on.

If I was with a group of people and someone i knew had their zipper down, well if it was all guys (all my fiance's friends) i'd probably just ignore it, I wouldn't want my fiance to think I had looked on purpose. If it was my fiance, I would tell him his barn door was open and probably hug him so he could fix it for himself without people really thinking anything. Now if it was a superior, I don't know if I could say anything.

well u should message ur boss n inform him about it

I'd do the same thing you did...just ignore it. I'd feel really shy telling him although I think it would be best to tell him. if you cant tell him directly...just make a sign or pass him a note