Hmm...only a few come to mind. :O!
1. Fake spider.
2. Whip cream on hand while he sleeps.
3. Scream, have him run in and hit him with something soft.
4. Buy something cheap for electronics that he would care about and then proceed to break it (might be too cruel however.)
5. Tell him your pregnant....okay, maybe not that one. >.>; Humor is subjective after all.
6. Hot sauce on the toothbrush.
7. Rocks in his shoes.
8. Some type of Oyster juice in his drink. (But he might not notice this one.)
Well that's all I can think of at the moment. :O! Maybe there is some type of pranking site that can give more and much better ideas.