Means “right now”.
“RN” is an abbreviation for “right now”. It refers to something happening in real time.
I’m feeling so hungover rn.
Sorry can’t pick you up rn.
Sometimes, when I'm about to go to sleep..I look back on my day and wonder what the heck I've gotten myself into. #happeningrn
— Sir Joseph Dirt (@EdgarAllenCrowe) January 11, 2015