round the bend
gila
funny in the head
batty
meshugge
one fry short of a Happy Meal
madperson
cracky
daft
up the wall
jimjam
bugfuck
berko
three stops short of Dagenham
toys in the attic
toppy
doolally tap
crazy as a pet coon
mad as a hatter
mad as a mongoose
cracked as an egg
bananas
siao
bonkers
tomfool
mad as a box of frogs
screwy
rocket
stunod
nuts
cuckoo for Cocoa Puffs
bats
kee siao
fruity
nutzoid
off one's rocker
nut-bar
gone fishing
off one's onion
off the beam
off one's dot
inane
fatuous
asinine
distraught
wackadoodle
insane in the membrane
not right in the head
loony tunes
daffiness