It's a Japan thing. Apparently, it's from anime. Senpai means someone you're suppose to look up to. (in this case a senior or a teacher if you're thinking of that chick from Misao who liked her teacher.) All in all 'Notice Me Senpai' means you want someone older than you to like you.
Person 1: "Give up, he doesn't like you."
Person 2 (to their senpai): "NOTICE ME SENPAI!"
by Idekman January 25, 2014
Used by 12 year old when making fun of furrys
Jupiter _kittys:OwO notice me senpai
EmoFurryQueen36: N o

Jupiter _kittys:Awh okay :(
by aRandomNoob7 November 15, 2020