v

whack out of one's brain (andreon); go mental (Taras); get hooked on (на ком/чем-либо Vladimir); go daft; go mad; crack one's brain; go off the hooks; go balmy; go dotty; go potty; heat; went over the edge (подвинуться рассудком Interex); be off one's nut; crack brain; blow one's top (He must have blown his top to make such a fool of himself. Вадим Александров); go cuckoo (Artjaazz); completely nuts (alex1unique); be mentally deranged

Игорь Миг

go nuts

argot.

slip one's trolley; slip trolley; slip one's trolley (slang To become insane; to go mad. Usually used jocularly or sarcastically. • My poor granny is starting to slip her trolley. She called me Darlene the other day–that's the name of her dead cat!

thefreedictionary.com); nut up (Anglophile); go bananas (highbery); lose one's marbles (lavagirl); slobber over (на Andrey Truhachev); slobber (over; на Andrey Truhachev); flip out (Taras); part one's mooring (delta); be off one's chump (Bobrovska)

figure d.

go round the bend (Leonid Dzhepko)

Gruzovik, figur.

deviate; decline; fall; sink

Gruzovik, inform.

go off one's head; go astray; go wrong

idiom.

be off one's beam (VLZ_58); be off one's rocker (What?! Is he off his rocker? -- Он что, спятил / свихнулся? ART Vancouver); go bananas (о животных; в прош. вр. • 'We were on one side of the creek, the creature on the other and our horses went crazy. Roger's little horse just went bananas.' (Bob Gimlin in an interview to Seattle Post, 1985) -- Лошадка Роджера точно свихнулась ART Vancouver)

inform.