Yeah, completely random, but I thought I'd publish this for fun.

1. Around the bend
2. Banannas
3. Barmy
4. Bats in the belfry
5. Batty
6. Belongs in the funny farm
7. Berserk
8. Bonkers
9. Brainsick
10. Buggy
11. Cracked
12. Cuckoo
13. Daffy
14. Demented
15. Disturbed
16. Escaped from the loony bin
17. From the nuthatch
18. Goofy
19. Has a screw loose.
20. Has kangaroos in the top paddock
21. Has some kinks with reality
22. In Bizzaro world
23. Loony
24. Loony tunes
25. Loopy
26. Lost his marbles
27. Manic
28. Mental
29. Moonstruck
30. Nutty as a fruitcake
31. Of unsound mind
32. Off his gourd
33. Off his rocker
34. Off his trolley
35. Out of his tree (and running around the park)
36. Out to lunch
37. Owns a straightjacket
38. Potty
39. Psyco
40. Reality-challenged
41. Screwball
42. Stark raving mad
43. Talking to the fairies
44. Unglued
45. Unhinged
46. Unzipped
47. Wacked
48. Wacko
49. Zany

And the favorite of everyone on this spot:

50. Mad as a Hatter