These are phrases that stop you from doing something stupid, or at least alert you that there is a problem in a positive way. Unlike KillerPhrases or AlarmBellPhrases, the person uttering them is aware rather than ignorant of the open manhole in front of him. Usually they stop work/effort/discussion in it's tracks, but it's a good thing because you entered the time-wasting zone.
That probably wasn't very clear, how 'bout some samples instead:
"It's 2AM" - implies everyone is in the veggie zone, and it's pointless to continue trying to come up with 'good' ideas, silly is all that's left.
"NO KILL I" - points out that the text under scrutiny is too ambiguous for any meaningful interpretations.
"Where is your test?" - When PairProgramming and about to add functionality.
What about a TitForTat page, with a list of pairs (KillerPhrases ,AntiKillerPhrases)? -- FridemarPache