Lori's Raection is justifiable but she is still annoying
The only way to rationalize Lori's reaction to Rick's confession is by arguing that she was very upset that Rick failed to play the peace maker in the rick/shane conflict and instead opted to let the chips fall as they may which ultimately resulted in the death of a man that Lori had feelings for: Shane.
It is true that Rick's indecision over the Randall incident was really a byproduct of the whole "I make better decisions than you" conflict with Shane, afterall, it was shane who wanted rick to kill randall and one would assume that rick's hesitation was in part due to his good morals and in part due to his ego and unwillingness to do it Shane's way. And as a result, it was this indecisive stance that pushed Shane over the edge and resulted in his death.
But the thing is this; it is hard to blame Rick for not actively doing something to address the conflict with Shane. His best friend and wife had an affair and the baby may actually be Shane's. And to make matters worse, Shane was also starting to act like an active participant in all Grimes family decision making.
Lori on the other hand is another matter altogether. Even though her behaviour is justifiable, her character still comes across as very annoying or at least rather poorly written. I mean, her husband just told her that he was almost killed and shouldn't his safety trump everything else? Well, apparently not judging by the way she reacted.
The only conclusion I draw is that Lori is an adulterous beach who would have been equally as happy with either Shane or Rick. Hence, Rick's announcement that he almost died having zero weight.
