Maybe I was 10 or younger. I still remember what I saw that day.
I lived in 5th floor on average apartment.
We had 3 rooms and one of them was mine.
It's about late night.
I opened up my room door to get in then I saw cigarette smoke shaps disappearing in front of my eye.
Maybe it was ghost shape or maybe it was moisture / mist like shape caused by room temperature changing while I opened up the door.