todd: dude, i've been texting you all day, why didn't you answer?  mike: sorry bro i've been so borderline nocturnal lately that i couldn't check my phone until now
staying up so late over winter/spring/summer break that you are sleeping through almost the whole day
"todd: dude, i've been texting you all day, why didn't you answer?  mike: sorry bro i've been so borderline nocturnal lately that i couldn't check my phone until now" What is the definition of "borderline nocturnal"?