Yes, people generally feel insecure before blind dates, at least from my experience. And it was implied she sat there with him for awhile and he was acting sleazy and annoying. What do you expect, them to have an hour long conversation in a music video for a song that's less than 5 minutes?The girl looks at herself in the mirror, and see herself overweight and short, I guess she have to deal with insecurity, than he meets a supposedly ugly guy and without even thinking she left him there. The hypocrisy is too strong. Imagine now if the girl was (for example) ShinDong and the "ugly" guy was an "ugly" girl, can you imagine the comments? Anyway, the song is ok/nice but I expected much better from her and Gaeko.
It's a cute play on the experience a lot of Koreans have when their friends set them up with blind dates. The "ugly guy" is a caricature of the typical sleazy, arrogant, annoying blind date that people are worried about meeting.
Edit: And anyway, watching it again she received a text from the guy she was supposed to meet asking where she was. That's when she leaves and she replies saying she'd gone to the wrong cafe by accident.
The first guy was just some random in a cafe coming up and asking for her phone number.