I love harmony, I love to harmonize. And I don't have a problem with someone in the audience harmonizing along, as long as it's ON KEY:)

But I find it really difficult to stifle myself whenever I'm at a concert; it's almost instinctual. I can hear the "holes" in the harmonies and I automatically find that missing harmony and hum along. However, I've learned to figuratively "stuff a sock" in my mouth because although I may be obsessed with harmonies, others may not be. Doesn't quite stop me from humming that missing harmony under my breath on the final note, tho'.