explanation of “bring your own girls”
Many Chinese people see bars and clubs as shady places where people of questionable character congregate, which is part of the reason why the boyfriend is a little put off when his girlfriend seems so excited about going to the club.
Some such clubs are staffed not only by bartenders and bouncers, but also by women (in this case, the “girls”), who chat with (and sometimes do more with) men who buy them drinks. The girlfriend cleverly responds to her boyfriend by pointing out that while he may have to spend money on drinks at the club, he doesn’t have to spend money on women at the club. Instead, he can bring his own girl.