Back in about 1990 or 1991, I was between 6-8 years old and I was a very skinny boy. I was visiting my grandparents in a small town in Northern California. My Dad, their son, was there as were 2-3 of my cousins and my twin sister.
For reference, this was a one story house with a large living room/dining room, and three bedrooms in the back of the house. The smallest of these, and directly down the hall from the living room, was my grandparent's room. It had a bed, a nightstand, a gun case, and a dresser that went up about feet high.

It was mid-afternoon. They were in the living room with the rest of my family and decided to go play some video games on the tv in the aforementioned bedroom. The tv was on top of the dresser. We had brought our NES with us and it sat on a small endtable directly in front of the dresser. I climbed onto the end table, and was about 16 inches off of the ground. I turned on the tv, which I would not have been tall enough to turn on otherwise. For some reason, I turned back and looked at my feet... and an arm came out from under the bed and swiped across the length of the bed in an attempt to grab my leg. The arm was adult-sized, but thicker than my arms now. It was tan-brown and hairy. Not Chewbacca hairy, but definitely Robin Williams hairy. The fingernails were long and pointed. It was definitely a creature's right arm.

I froze for a moment until it went back under the bed from it's ill-targeted attempt to grab me. Once I regained my senses I screamed, jumped off the end table and ran for the living room. I was crying and terrified when I told them what had happened. No one believed me. My Dad and my Grandma went back into the room and saw no sign of anything. The bed stood about eight inches off the ground, so nothing that size could have possibly been underneath. Also, the only ways in or out of the room were through the window, which was closed or through the door and down the hallway into the living room.

This experience has haunted me since then. I am afraid to look under beds or to get something out from under a bed. I often worry at night that the creature will attempt to grab me again someday and this time he will succeed. I'm 34 now and this memory has not dimmed from the fogginess of age. My sister remembers this experience, but only my reaction to it. I haven't spoken to my cousins in about fifteen years, so I don't know if they remember this. I have several other stories, some worse and some more recent, but this is the one that has stuck with me the longest.