Of course theres the most blatant tipoff that your story has come fresh out of the overactive imagination of a 12 yearold with a hard cock who hasnt yet passed his english exams -- namely, grammar, or lack thereof:

"His hot stiff one slide into me and pleasure ahh yes I have much!!!"

You might think I'm just being stupid, but I recently read a story (someone forwarded it to me, its not like I go out on usenet looking for such crap!) and the grammar was just so appalling it took the whole story to the point of being an absolute joke!

Update:
Here it is, I found the one that inspired me to write this:

  • By 10 AM she was already inside a teen clothes' store in a nearby mall, a place specialized in female teen garment, with lot's of sexy stuff.
  • The straps were very thin and constantly rided down her shoulders, sometimes falling in her arms
  • Since it was a large top her hooters were exposed when she bended or even arched her back a little more than usual
  • The girl was also wearing the micro skirt she had just brougth
  • I felt very sexy in my outfit and was crazy to test it's effect on men.
I think you've heard enough...

Unless of course, you have a bad grammar fetish... grin