Responses
I'm guessing before he crafted his "BJ Alex" and 'Student president Jiwon" persona's, he wasn't the calm, collected, smooth and boastful man he presents himself as now. Maybe Jiwon is annoyed at MD, because MD saw this "real" side of Jiwon that time they went out drinking. Also, in all of the flashback scenes with Jiwon and his ex partner, it seems like Jiwon is the green one who is getting told what to do, and is being taken along rather than this dominant person he tries to be now.
Alex is probably embarrassed asf because he threw a jealousy tantrum over his “non-romantic sex partner” XD
Jokes on u Alex, we see u catchin those feels