Perhaps you're right, Jackie. Thanks for at least trying to guess. :-)

I've noticed that, in countries other than the U.S., people whistle when in crowds when they are displeased instead of booing. Here they usually whistle when they are pleased, but I think the whistles sound a bit different.

I'm really curious about "Boo!" in the context of displeasure. Boo is not in my book of etymology at any rate.