go in off the deep end

1. To become crazy or irrational. (An allusion to the area of a swimming pool where the water is the deepest, and thus the most dangerous.) Primarily heard in US. A: "Now your father thinks the neighbors are plotting against him." B: "Wow, he's really gone in off the deep end!" You've definitely gone in off the deep end if you're peddling conspiracy theories now! You can't tell people you want to start a business selling bees as pets—they'll think you've gone in off the deep end.

2. To become extremely or uncontrollably angry. Primarily heard in US. Whoa, man, stop yelling! I only put a tiny scratch on your car, so there's no need to go in off the deep end. You're failing three classes? Whoa, Mom and Dad are gonna go in off the deep end when they find out! If you're honest with the boss about your mistake, maybe he won't go off the deep end.

3. To become carried away (with an action or idea) in a reckless, irresponsible, or inappropriate manner. Primarily heard in US. I thought Karen just wanted to do some minor renovations around the house, but she's really going in off the deep end with it! You two got married in Vegas last weekend? Have you gone in off the deep end? A: "Why would he openly flirt with one of his subordinates?" B: "I know, it's like he's gone in off the deep end."