When I was in grade school, I would sometimes have trouble falling asleep. On these occasions I would usually just lie there in bed, waiting to feel sleepy. My bedroom had a night light in it, so the room and everything in it were plainly visible.
One night I was lying there, sometimes with my eyes closed, sometimes with my eyes open. I noticed after a while that when I opened my eyes, it looked like something moved in a part of my room. I thought it was just due to my eyelashes or my eyes adjusting to the night light. Several minutes later I had changed position slightly, but now I noticed that the apparent motion was in the same part of the room, and was no longer at the edge of my vision. It looked like something was ducking behind the bean bag chair in my room. I began to experiment with this by closing my eyes for a few seconds and then opening them to look directly at the bean bag chair, and I continued to see a brief flash as if something had quickly ducked down.
After testing this a few times, I had the idea of opening my eyes just a crack and peeking at the bean bag chair. What I saw looked exactly like those images of "Kilroy was here", except this was not just peeking over the bean bag chair but fully visible down to the shoulders. You could also say it looked like the "Alice the Goon" character from Popeye cartoons. It was about three feet tall, pale, and while not glowing, it appeared somewhat luminescent. It was looking right at me with wide cartoonish eyes. I closed my eyes fully again and prayed until I fell asleep.
I never saw a creature like this again, and nothing else happened in my bedroom. By now I knew better than to tell my family about what I saw. Years later I have told the story to see if anyone had a similar experience. One person told me a story about the Kilroy lifting above the wall and revealing a mouth full of pointed teeth, but it was not experienced by the person telling me and I do not remember the circumstances of that story.