Yep. I've seen people plop down right in the middle of a fairway, and when we tell them it's a DG course, they say something like "Why can't we both enjoy the park?" Because if you get hit by a flying disc, you'll be 'enjoying' serious injury if not worse.
And then we had a young couple that liked to put up a hammock in the wooded part of the course, but right in the throwing lane...
I play Schenley occasionally. I've basically come to accept the fact that if I'm there on a weekend I will likely have to skip holes 1 and 2.
It is a multi-use park after all, and holes 1 and 2 basically go right over top of the prime picnicking, sun-bathing, kite-flying, etc. area. Generally if someone is anywhere near my throwing lane, I'm not going to throw for fear of injuring them, even if unlikely. Not to mention that trying to make sure I avoid someone pretty much guarantees I'll make a bad shot.