Okay, so we can't be 100 percent positive that these are from "actual" student papers. [Update: They are not.]
1. His thoughts tumbled in his head, making and breaking alliances like underpants in a dryer without Cling-Free.
2. He spoke with the wisdom that can only come from experience, like a guy who went blind because he looked at a solar eclipse without one of those boxes with a pinhole in it and now goes around the country speaking at high schools about the dangers of looking at a solar eclipse without one of those boxes with a pinhole in it.
3. She had a deep, throaty, genuine laugh, like that sound a dog makes just before it throws up.
4. Her vocabulary was as bad as, like, whatever.
5. He was as tall as a 6-foot, 3-inch tree.
6. The little boat gently drifted across the pond exactly the way a bowling ball wouldn't.
7. From the attic came an unearthly howl. The whole scene had an eerie, surreal quality, like when you're on vacation in another city and Jeopardy! comes on at 7:00 p.m. instead of 7:30.
8. The hailstones leaped from the pavement, just like maggots when you fry them in hot grease.
9. Long separated by cruel fate, the star-crossed lovers raced across the grassy field toward each other like two freight trains, one having left Cleveland at 6:36 p.m. traveling at 55 mph, the other from Topeka at 4:19 p.m. at a speed of 35 mph.
10. John and Mary had never met. They were like two hummingbirds who had also never met.
11. He fell for her like his heart was a mob informant, and she was the East River.
12. Even in his last years, Granddad had a mind like a steel trap, only one that had been left out so long, it had rusted shut.
13. Shots rang out, as shots are wont to do.
14. The plan was simple, like my brother-in-law George. But unlike George, this plan just might work.
15. The young fighter had a hungry look, the kind you get from not eating for a while.
16. He was as lame as a duck. Not the metaphorical lame duck, either, but a real duck that was actually lame, maybe from stepping on a land mine or something.
17. The ballerina rose gracefully en pointe and extended one slender leg behind her, like a dog at a fire hydrant.
18. It was an American tradition, like fathers chasing kids around with power tools.
[These metaphors and similes came from the Washington Post Style Invitational Bad Simile and Metaphor Contest.]