spaced-out, forgetful, absent-minded

れっぽい(わすれっぽい) Describes someone’s personality:absent minded; someone who always leaves their umbrella on the train.   $$$
ぼんやりしてる To space out. – to be all ‘duh.’ Describes a specific action – even the most lucid person sometimes does ぼんやり-
れる(わすれる) To forget something – not limited to physical objects like 忘れっぽい。
すせない(おもいだせない) To be unable to remember something (like a word, your Dad’s birthday, or a Kanji!)