There is this guy in the office that constantly walks around whistling loudly all day long. He doesn't seem to realize that it's distracting and that others including myself find it to be incredibly irritating. However, no one has said anything to him so far. How would you deal with a situation like this?
I don't recommend coming to him and telling him that it's been bugging you for a long time or that anyone else doesn't like it. Instead, on one particular occasion, say something like:
Bill, I'm trying to [difficult task] and that whistling is going right through my head. Can I ask you not to?
He will probably comply, then absent mindedly whistle again later. When it bothers you, you can now say something like:
I'm having another can't-hear-whistling day, Bill
Eventually he will learn that you can't stand whistling at all, or what level of it you can stand, and he may hear similar things from others and stop whistling at work at all.
Some people whistle when they're relaxed and happy. It would be sad if he felt less happy at work because people were asking him not to whistle. But it would be sadder still if he came to realize that you had been seething about it or discussing it with others. Just react in the moment as many times as you need to, until it doesn't bother you any more.
Or wear headphones.
Drop him a quick email saying you find his whistling distracting and ask him politely to tone it down.
If that doesn't work you can escalate it to management but 99% of the time a polite email (so he doesn't lose face) will sort everything out.