1) Absolutely ludicrous 2) Absolutely ridiculous 3) Absurd 4) Amphigoric 5) Asinine 6) Bananas 7) Beyond belief 8) Beyond illogical 9) Birdbrained 10) Brainless 11) Characterless 12) Cockamamie 13) Cockamamy 14) Cockeyed 15) Completely absurd 16) Completely ridiculous 17) Crazy 18) Cuckoo 19) Daffy 1) Absurd 2) Apish 3) Asinine 4) Daffy 5) Devoidofmeaning 6) Dumb 7) Empty headed 8) Fatuous 9) Foolish 10) Goony 11) Idiotic 12) Insensitive 13) Pless 14) Senseless 15) Silly 16) Simplistic 17) Stupid 18) Useless 19) Vacuous 
• (a.) Without contents; empty; void of sense or intelligence; purposeless; pointless; characterless; useless. • (n.) That which is void or empty.
International Academy of Nursing Editors
In·ane' adjective [ Latin inanis .] Without contents; empty; void of sense or intelligence; purposeless; pointless; characterless; useless. 'Vague and inane instincts.' I. Taylor. -- In·ane' noun That which is void or empty. [ R.] « The undistinguishable inane of infinite space.» Locke. 
silly senseless 
lacking sense, significance, or ideas; silly: inane questions. · empty; void.
[SAT terms] devoid of intelligence