You wave at Mingi as he walks into the class and you attempt to say hi to him, but he merely walks past you to his seat, which just so happens to be located behind you, and he doesn't even glance in your direction. You are disappointed but still attempt to smile at him.

Just as you are about to utter a simple "good morning", Mingi immediately delivers the devastating line “I already have a girlfriend, so stay away from me”

In truth, he has no such girlfriend, and he was simply lying in order to make you stop pursuing him. He was simply too lazy for a relationship and believed you would fall for his lie.