Center for Sleep Study
Trappist monastery?
Within 100 meters of other living creatures
(but i’m really not at all good)
On a park bench right outside the county courthouse (directly under a courtroom window). True event - playing fife in this very location I looked up when I heard pounding to a sea of angry faces…including one in black robes shaking his fist at me!
Eric
In the main office of my water treatment plant during weekdays (which is why I love night shift).
Onboard Amtrak.
I should have added…anywhere anyone can hear me. 
Anytime at home when my spouse has either Oprah or Dr. Phil on the television. But just because I am not allowed, does not mean that I quit playing the whistle, I just go to another room and play louder! 
{As an aside, it is wondrous how much squawking a whistle can do when Oprah is pontificating. I know that the purpose of practice is to eliminate squawking but when she is on television, I just cannot help it!}
Brewster MA on Cape Cod. I sat out on a deck at a rented house playing the Brass Burke and a lady about 500 yards downhill called on the phone and threatened to call the police and the “association” for that “flute-thing.”
Couldn’t I go inside, she said? Wrecked a beautiful morning in a way. My first taste of East Coast hospitality.
In a very old, thus very slow, small elevator in a historic hotel. The place we were to be playing in was a ballroom at the top of the hotel. I went up alone with all the sound equipment (there was no room for anyone else) and started playing. Kind of a cool echo-y sound but a few residents of the hotel were less than appreciative.
Rap concerts and operas - possibly the only thing the two have in common.
In a library. Except, quite possibly, at the library where MarkB works and when he is on duty!!! 
In the stairwell of Church Hall (a dormitory) at the University of Georgia.
I was listening to an article thingy on the radio about the similarities of rap and opera (using sound examples of both). It was really cool, and about the only time I have come close to respecting rap as art music.
I would repeat some of it, but I have forgotten most of it.
One quick thing: the guy compared the arias in opera to something similar in a rap song, (a fairly popular one that plays on most radio stations). Like I said, pretty cool, at least from a sort of musicologist point of view.
I work in a library and lots of time you wouldn’t be able to hear someone playing the whistle in there, it gets pretty noisy! … libraries aren’t the quiet, stuffy places they once were, at least not the one I work in!
another place that comes to mind…
at an orthodontics appointment
A colonoscopy might not be a good time to work on that pesky 3rd octave. 
-This is speculation, but mourners at funerals might be unappreciative of a peppy whistle sound. OTOH, Dixieland funerals have a well known celebratory aspect, and some would go for it. A poignant air might do in other cases.
-As Mark Twain wrote concerning funeral etiquette: “Do not bring your dog.” (This has always been a disappointment to me. A person mourned by dogs has by definition led a life worthy of emulation.)
Every once in a while, I find myself alone on a MUNI (San Fran) bus, and I am tempted to play. I mean, it’s just me & the bus driver. But I haven’t done it yet. Seems too weird. Well, one of these days.
There’s a few places I’ve hestitated but went right ahead anyway. At the Golden Gate Conservatory of Flowers. Winery garden up in Napa. Outside at the Getty museum. The Golden Gate Bridge (the wind made it tough). Places that are either semi-private or where you pay to get in.
But hell, it’s JUST whistle music. I mean, it’s not a trumpet or zurna–nothing too loud or disruptive. Outdoors, most people can just tune me out if they want.
I’d rather face the the irate driver of a city bus, or all the spinsters of Cape Cod, than…
125 recorderplayers playing on alt-, tenor-, and bassrecorders: ‘BACH in Dokkum’
Wasn’t the funeral procession in “Waking Ned Devine” led by someone playing a Generations-type whistle?