GuyRule #386.1: Food Manipulation
The food of a guy can be messed with only under certain circumstances:
1. The target must not be present
2. All people present must agree that the target is an asshole
3. The punishment issued is funny, but not life threatening
4. No one present can reveal the joke
By following these guidelines, you get your revenge on the target and he doesn't suspect a thing. These guidelines must also be followed if executing the punishment on a chick, but only if she truly deserves it, like for unfairly defaming your character or criticizing your performance in the sack or insulting your manhood. Also, be creative; water down or "tea bag" his drink, put napkins in his sandwich, loosen the tops of the salt and pepper shakers, put stuff on his seat while he's gone, put boogers in his burger, etc. Best of all make it look like an accident if you can; he'll be even more embarrassed if he thinks the only person to blame is himself!