@rediscover In this particular case, the MC probably never had a girlfriend and probably didn't interact much with people of his own age, considering how he is a high school dropout who only focused on working all the time after the accident. I don't find it hard to believe that he would be awkward around a woman (maybe not this much, but his reactions are exagerated for the sake of comedy).
The thing about MCs and female contact is definitely a trope, don't really know the reason why it's so prominent, though.