loony

Example:She had always been a bit crazy, but now she was truly off her rocker.

Definition:having or showing a lack of sound judgment; eccentric, insane, or foolish.

Example:He had a mad idea to attempt the impossible climb on his own.

Definition:suffering from a milder degree of insanity or derangement.

Example:After the accident, he became insane and needed to be kept in a secure mental institution.

Definition:mentally deranged or troubled; afflicted with a serious mental disorder.

Example:His idea to build a treehouse in his backyard was nuts, but hey, we all have our quirks.

Definition:mildly insane or crazy (slang); eccentric, mad, off one’s rocker, batshit.

Example:Ever since he proposed that he not pay rent for a year, Tom has vanished from the face of the earth.

Definition:often said sarcastically, to mean someone has disappeared or gone mad; typically used for someone who is difficult to find or gets lost.