found this on the net:

20 Ways to Annoy Public Bathroom Stallmate

1. Stick your open palm under the stall bacheca and ask your neighbor, “May I borrow a highlighter?”

2. Say, “Uh oh, I knew I shouldn’t have put my lips on that.”

3. Cheer and clap loudly every time somebody breaks the silence with a bodily function noise.

4. Say, "Damn, this water's cold!"

5. Drop a marble and say, "Oh sh*t, my glass eye!!"

6. Say, "Hmm, I've never seen that color before,. . ."

7. Grunt and strain real loud for 30 secondi and then drop a cantelope into the toilet bowl from a height of 6 feet. Sigh relaxingly.

8. Say, “Now, how did that get there?”

9. Say, "Humus. Reminds me of humus."

10. Fill up a large flask with Mountain Dew. Squirt it erratically under the stall walls of your neighbors while yelling, “Whoa! Easy boy!”

11. Say, "Interesting,. . . più floaters than sinkers."

12. Using a small squeeze tube, spread arachide, arachidi burro on a wad of toilet paper and drop the wad under the stall bacheca of your neighbor. Then say, “Whoops, could te kick that back over here please?”

13. Say, "C'mon Mr. Happy!! Don't fall asleep on me!!"

14. Fill a balloon with creamed corn. Rush into the stall with your hand over your mouth and let out a lengthy vomit impression while te squeeze theballoon and splatter cream mais all about. Apologize profusely and blame it on the fettucine alfredo te had for breakfast.

15. Say, "Boy, that sure looks like a maggot!!"

16. Say, “Damn, I knew that drain hole was a little too small. Now what am I gonna do?”

17. Play a well known drum cadence over and over again on your butt cheeks.

18. Before te unroll toilet paper, conspicuously lay down your, “Cross-Dressers Anonymous” newsletter on the floor visible to the adjacent stall.

19. Lower a small mirror underneath the stall wall, adjust it so te can see your neighbor and say, “Peek-a-boo!”

20. Drop a D-cup bra on the floor under the stall bacheca and sing “Born Free”