It should happen all the time.

Every time there's a politician speaking in front of a crowd, everyone in that crowd has a couple of projectiles strapped to their feet.

You probably can't smuggle in a bag of rotten tomatoes, or a pie, let alone some kind of weapon, but there you've got those two things right on your feet.

Maybe you get in there and you decide, hey you really like your shoes, you don't want to lose one, so you find something else. A pair of sunglasses. A watch. A hat. Maybe you look around and find something at the venue, like a little plastic display placard.

First of all, none of those things are going to throw as well as a shoe. You're going to sacrifice your distance and your accuracy just because you don't want to walk home with one shoe. Well there's no point in doing shit if you're going to miss, so better to just use the shoe.

Second of all, the shoe is a clear message. You throw your watch up there, he's likely to say hey thanks for the great watch. Even if you threw both of your shoes, they might say hey thanks for the free pair of shoes. But if you throw just one shoe, that's a clear fuck you.