Generally silly/scatterbrained:
* Goofy: This term is generally lighthearted and playful.
* Ditzy: This term implies a lack of intelligence or common sense, often used for women.
* Spacey: This term suggests someone is absentminded or lost in their own world.
* Clueless: This term indicates someone lacks awareness or understanding of a situation.
* Airheaded: Similar to ditzy, this term implies a lack of intelligence or thoughtfulness.
* Daffy: This term is playful and suggests a slightly eccentric or whimsical personality.
* Wacky: This term suggests someone is unusual, eccentric, and often amusingly unpredictable.
* Bonkers: This term is playful and suggests someone is a bit crazy or off-kilter.
More negative connotations:
* Dopey: This term suggests someone is stupid or slow-witted.
* Dimwitted: This term is more derogatory than dopey and implies a lack of intelligence.
* Brainless: This term is highly insulting and suggests someone is completely lacking in intelligence.
The best word to use depends on the context and the tone you want to convey. Remember that some of these terms can be offensive, so use them with caution.