When someone receives sexual pleasure primarily from someone else's social media pictures - especially Instagram - with or without having any other kind of relationship with that person, especially when the person who the social media account belongs to is openly in a sexual relationship with someone else. Essentially, when someone cuckolds themselves via another person's Instagram.
to instantly find yourself fawning over that one hottie with the sparkling eyes, and that beaming smile. you probably don't know their name, and they probably don't know yours, but who cares its infatuation at a first glance. its not necessary to know much about that person, besides the fact that they're oozing in appeal.
Guy1: " oh man did you see that waitress over there? "
Guy2: " you mean the one in the miniskirt?! hot! "
Guy1: " No shit."
Guy2: "instacrush dude, instacrush. "