1. the quality or state of being stupid, foolish, or lacking intelligence
Usage: uncountable; informal
2. the quality of acting without thought or consideration; lack of mental effort
Usage: uncountable; informal

Examples

• His brainlessness was evident when he forgot his own phone number.
• The brainlessness of the decision surprised everyone on the team.
• She criticized the brainlessness of the plot in that action movie.
• His brainlessness led him to make the same mistake twice.
• The brainlessness of rushing into the project without planning caused problems later.
• I can't believe the sheer brainlessness of leaving the keys in the car.