I live in a flat with a big shared (with 20-odd neighbours) front and back garden. The front garden is easily accessible though a small gate/stepping over a low wall. My neighbours and I jointly own the garden - it's private property and we pay for its maintenance.
The flats are opposite a sports club used as a creche during the day. A lady who I assume works there regularly (like, hourly), wanders into our garden for a cigarette. She normally hides behind a tree (presumably it looks bad to smoke outside the creche).
It irks me. It's private property. Sometimes she is joined by a colleague or two. I'll check for fag butts next time I go outside but it wouldn't surprise me if she left them behind.
AIBU to think about asking her not to smoke in a privately-owned garden? (I don't like smoking much, obviously).