go off the deep end

go off the deep end & jump off the deep end

1. Lit. to jump into a swimming pool where the water is over one's head and one needs to be able to swim •

You are still only learning to swim. Are you ready to go off the deep end?

•

He jumped off the deep end where he would make a bigger splash.

2. Fig. to become deeply involved (with someone or something) before one is ready. (Applies especially to falling in love.) •

Look at the way Bill is looking at Sally. I think he's about to go off the deep end.

3. Fig. to act irrationally, following one's emotions or fantasies. •

Now, John, I know you really want to go to Australia, but don't go jumping off the deep end. It isn't all perfect there.

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or[go overboard] {v. phr.}, {informal} To act excitedly and without careful thinking. * /John has gone off the deep end about owning a motorcycle./ * /Mike warned his roommate not to go off the deep end and get married./ * /Some girls go overboard for handsome movie and television actors./