spaced-out, forgetful, absent-minded

忘れっぽい(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-

忘れる(わすれる)	To forget something – not limited to physical objects like 忘れっぽい。

思出すせない(おもいだせない)	To be unable to remember something (like a word, your Dad’s birthday, or a Kanji!)