Bloodshot eyes as a result of smoking weed. Something to do with THC doing something with your blood vessels in your eyes or something, I can't remember properly because I was stoned when I read it. But yeah, when you smoke weed your eyes normally go red, this is red eye.
DUUUUDE! YOU'VE GOT EPIC RED EYE!!!
That bitch got stoned last night, you should have seen his red eye! He was like Darth Maul or some sh*t!