I didn't believe in ghosts. At all. One of my friends told me she used to see her grandfather's ghost when she was younger. And I told her she was delusional and probably had a brain tumor or something. All that changed when I saw a ghost myself. I'll never forget it. I was 19 years old, in my first apartment with a room mate.
It was an old 6 unit apartment building, 3 units on each side. We lived in the top unit on the right. It was built in the 1920's. Soon after I moved in, sometimes I'd hear the weirdest thing - I'd hear kids playing outside - at 3am. Little kids laughing. I could never make out words. Who let's their little kids play outside at 3am? I found it weird, I could never see any kids outside, but I figured it was dark and the angle from my window meant I couldn't see half the backyard, so, it was possible they were in that part of the yard.
A few months after I moved into the building, the middle unit on the left side became available, at a super good price, and a friend and co-worker and his girlfriend moved in. This building had an addition made to the back of the building in the 1940's. In their unit, it had never been finished- it was still just old wood with no insulation, a storage room. This meant it was FREEZING in the winter, but when summer came it was a nice cool spot, and my neighbor set up his TV, some chairs and a coffee table in there.
One night his girlfriend was at a family thing, my room mate was out and it was just the 2 of us drinking beer and watching movies in the storage room when I looked over at my neighbor and he had passed out. He was a HEAVY drinker and this wasn't all too uncommon. I had only had a few beers. I decided to stay and watch the end of the movie, then let myself out. When I looked back at the TV - on the coffee table there was a little boy. I felt a cold electric chill go up my spine!
The little boy was dressed in what looked like a suit. Dress pants, a vest, dress shoes. He was sitting with his head on his hands almost like the famous sculpture "The Thinker". The only difference is he was resting his forehead on his hands instead of his chin - and he was shaking his head in dismay.
Image credit: By AndrewHorne (talk) - Own work (Original text: I (AndrewHorne (talk)) created this work entirely by myself.), Public Domain, https://commons.wikimedia.org/w/index.php?curid=15582363
I didn't know what to think - my mind was locked. I could only stare. I knew there was no kid there. But - there was a kid there. Silently shaking his head in dismay at my passed out neighbor. I quickly got up, let myself out and went home, wondering if I had a brain tumor. I couldn't explain it. I fell asleep thinking about it.
The next day I went and knocked on my neighbor's door. When he answered, I asked him jokingly if he put anything in my beer. He was confused so I told him what I saw. His face went white. He called his girlfriend to the door and said "Tell her exactly what you told me" So I did - and her face went white. They told me to sit down.
They told me that when they rented the unit, the owner of the building told them a story. The owner told them that the reason the rent was cheap is she had a hard time keeping tenants, because often people had weird experiences. She went on to tell them that in the 1950's, that unit had been rented to a single mother.
The story they told me was the mother was an alcoholic. When her son got home from school - in his school uniform that looked like a little suit - she would lock him in the storage room in the back while she drank until she passed out. One day he heard his friends laughing & playing out back. He asked his Mom to let him out so he could go play with his friends. She said no, and he threw a tantrum. As she kept drinking, and he kept screaming and banging the door - she eventually lost her temper and in a drunken stupor, stabbed her own son to death. He died in the storage room, where I saw the little boy shaking his head at my passed out drunk neighbor.
Now it was my face that went white. The next time I saw my friend who used to see her Grandfather's ghost - I owed her an apology.
I feel blessed to have had that experience, it changed my life and opened my mind to more spiritual ideas. Many years later I'd face my own issues with alcohol. I'm glad to say I've been sober since April 9, 2012. Thanks 
"Gratitude" - 8 x 8 inches - Acrylic paint on stretched canvas - painted for a friend