Dic: go off the deep end

자료: http://www.answers.com/go%20off%20the%20deep%20end

Idioms:

go off the deep end

1. Become unduly excited, overwrought, or angry. For example:

• When he heard about John's smashing into his car, he went off the deep end. [c. 1920] Also see in deep, def. 2.
  

2. Be irrationally carried away, act irresponsibly or heedlessly. For example:

• Just because you like her looks doesn't mean you should go off the deep end and propose. [c. 1920]

In both of these colloquial usages deep end alludes to the deep end of a swimming pool.