"oh you screwed us! We should have been able to beat that troll easy!
Yeah, and thats why I'd tread very carefully here with changing rules (like saying no more ressurect or -2 CON or -1 level etc).
The players do not realize that they were being idiots and therefore feel that you were being mean to them. As long as they think having half the party fight a disadvantaged monster (Evil Wizard: "yes, he's charmed. so walk up behind him and let him have it! I'm going to go get a snack." LG Paladin: "Okay.") is a good way to min-max XP or that running away and letting a Troll eat a family of villagers is heroic ("Women and children first? What kind of rule is that!? Let me in the damn lifeboat!"), they're not going to understand why you are penalizing them for their stupidity.
And, after all, that is what you are talking about. The current penalties for stupidity in your game are not great enough; you would like to ratchet them up. Changing important rules in the campaign is always a touchy issue.
Tangent: I remember doing this exact same stupid thing in the campaign I played in when I was in high school. I fought an orc solo for the XP and got killed while the others watched. I remember being mad about it too, even though I was doing something really dumb. "I'm so unlucky, you hit twice and rolled two 8s! How unfair!" Ah, the folly of youth.