
I don't understand why in mangas they depict being virgin is shameful and made fun of.......

It's also like that in real life too. There were times, especially the guys, who made fun of each other about not having a gf, never holding hands with a girl, not having their first kiss yet, etc. I also had plenty of girl acquaintances who also teased about others not having done their firsts as well. They were also young.
I guess, as human beings, it's just in our nature to do so. ╮( ̄▽ ̄)╭
So this is the one that is turned into an anime ...*sigh*