"저 니마", "Jeo nima" I think it's kind of slang on the internet. When we call someone, we use "木叶丸 +nim". People want to say something fast on the internet. so usually just say "nim" instead of calling "name+nim" Also we don't know someone's name before introduce. That's why just say 'jeo nima'. I think meaning is similar with "Excuse me". but it's slang on the internet, I recommend you use 'jeo gi yo'.