To be off the deep end, or more commonly to go off the deep end, is to become so angry, nervous, or excited that you lose control of yourself and start to behave in a crazy or irrational way.
To be off the deep end 或更常用的是 to go off the deep end,是指生氣、緊張或激動的情緒,導致自己失去控制,開始做出瘋狂、不理性的行為。