Oh yes, others telling others to "smiiiiile" is quite common here. I can't count how many times I've heard it, and it's not like I walk around frowning or anything.

The last time it happened was a few years ago when I was at the horse hospital awaiting the vet's arrival to put my precious donkey to sleep after she'd been suffering in pain for a week while we tried to cure her. I was pacing around feeling really horrible about it when one of those smile police types walks around the corner, takes one look at me, and says "Smiiiiiile."

If I was the person I am now I'd let him have it with both barrels. Back then I just smiled a bit and walked away. It's a big pet peeve of mine, and at that time I swore I'd never again allow some ++###%# to manipulate me like that.