Keep calm and carry on
keep it real 
keep it up!
keep one's fingers crossed 
kewl 
KFB
kick it 
kick ass / kickass 
kickback
kicks 
KIK 【ベスト100スラング80位】
killer 
killin' it / killin it
kinda 
KOTD
Knock on wood!
kiss my ass 
kmt (Kiss My Teeth)
knock it off 
kosher 
kudos