怒氣填胸 He Turns His Cudgel On Them
只見那獃子和沙僧口裡嗚哩嗚哪說甚麼。行者怒氣填胸，也不管好歹，撈起棍來一片打，連聲叫道：「打死你們，打死你們。」那獃子慌得走也沒路。只见那呆子和沙僧口里呜哩呜哪说甚么。行者怒气填胸，也不管好歹，捞起棍来一片打，连声叫道：「打死你们，打死你们。」那呆子慌得走也没路。
逐句解 Line by line
He saw only that idiot and Sha Monk mumbling something or other in their throats.
那 is nà, 子 is the everyday unstressed zi in the nickname, and 甚 is shén. The two of them are talking, which means they have only just realised.
Pilgrim, his chest packed full of rage, cared nothing for right or wrong, caught up his cudgel and laid about him, calling out over and over, "I will beat you to death, I will beat you to death."
怒氣填胸, anger stuffing the chest, is a set phrase, and 不管好歹 is caring nothing for good or bad — that is, striking without judging who deserves it.
That idiot was so flustered there was nowhere for him to run.
得 is the unstressed de joining the fluster to its extent — flustered to the point of having no way out.
Pilgrim's response to failure is to attack his own brothers, and the novel does not excuse it. He cares nothing for right or wrong, which is the narrator's judgement and not his.
It is also, in fairness, not entirely irrational. He posted the two of them on the sick man precisely so this could not happen, and they let a fiend walk in and carry him off the mattress.
The detail that lands is Bajie having nowhere to run. This is a coward with real speed and enormous strength, and he is cornered in a courtyard by his own brother.