General:
* Futile: Pointless, unproductive, having no effect.
* Vain: Empty, pointless, without results.
* Absurd: Ridiculous, illogical, nonsensical.
* Inane: Foolish, silly, lacking in substance.
* Pointless: Having no purpose or value.
* Frivolous: Lacking in seriousness or importance.
* Meaningless: Lacking in significance or purpose.
* Unnecessary: Not required or needed.
* Superfluous: More than is needed or wanted.
* Needless: Unnecessary, not required.
Negative:
* Idiotic: Extremely stupid.
* Stupid: Lacking in intelligence or common sense.
* Irrational: Not based on reason or logic.
* Unreasonable: Not justifiable or logical.
* Foolish: Lacking in good judgment or sense.
* Brainless: Lacking in intelligence.
* Unintelligent: Not showing intelligence.
* Insensible: Unaware or insensitive to the feelings of others.
* Indiscreet: Lacking in prudence or good judgment.
* Imprudent: Unwise, reckless.
Descriptive:
* Rash: Acting or done without careful consideration.
* Impulsive: Acting suddenly and without thinking.
* Reckless: Careless of consequences.
* Arbitrary: Based on random choice or personal whim.
* Whimsical: Impulsive and unpredictable.
* Careless: Not showing care or attention.
* Thoughtless: Not thinking about the feelings of others.
Formal:
* Incoherent: Not clear or logical.
* Inconsequential: Not important or significant.
* Unproductive: Not achieving any desired results.
* Utter nonsense: Completely meaningless or foolish.
Figurative:
* A shot in the dark: A guess or attempt made without knowledge or information.
* A wild goose chase: A pointless pursuit.
* A waste of time: Something that is unproductive or pointless.
The best word to use will depend on the specific context and the tone you want to convey.