The only thing I can think of is that they didn't want him to freak out over just something that anyone would have freaked out over. For example a situation where it could be plainly seen that he was well within his rights to be angry. You know? Someone starts snarfing your food right in front of you, and just about any normal human being would be at least a little pissed off. So that wouldn't really prove anything. No, they needed to secretly piss him off but then publicly reveal the freak-out.
Granted, that is a pretty weak justification, given that the bugs-in-the-salad plan would have been an extremely justified freak-out, too. I dunno, though, maybe they were hoping that he would just completely snap and punch somebody?
To be perfectly honest, that whole book always struck me as being a little silly.
