I've had someone come in my gate and snip off my tulips. They just cut the blooms (very little stem) so I don't know what the point was. I told my mother and she said that decades ago there was a woman who would bring a little basket and go in all the neighbors yards to cut bouquets for herself.
Anyway, it only happened one year. After that I planted orange and yellow tulips which I guess they didn't like so they left them alone.