[monster]

1) Cocoa Puffs (cereal killer # 1)
2) Froot Loops (cereal killer # 2)
3) Whack job (or Piece of Whack)
4) Bananas
5) Crack head
6) Nuts
7) Bonkers
8) Off the deep end
9) Kooky
10) Ate up
11) Tweaker
12) Wing Nut
13) Wackadoo
14) Nut Bar
15) Twisted
16) Insane
17) Crazy
18) Pensive Pam
19) 'Round the Bend
20) Cuckoo
21) Sandwich short of a picnic
22) Not playing with a full deck
23) Lost their marbles
24) Got a Screw loose
25) Loopy
26) Off their trolley
27) Out of their mind
28) Gaga
29) looney tunes
30) Loopy (see what I did thar! Har)
31) Psycho
32) Mental
33) Off with the fairies
34) In Lala land
35) mental mental chicken oriental
36) bit of a mentalist
37) Nuckin Futs
38) Bats
39) Batty
40) Bats in the belfry (he/she has ~)
41) Two bricks short of a full load
42) Lights are on but on-one's home
43) Bedlam escape artist
44) Scrambled
45) Mad as a hatter