kompaA kompa is a drinking party popular among young people in Japan. Typically a guy brings a certain number of his male friends and a female acquaintance of his brings an equal number of her single friends.
The most common arrangement is three or four guys sitting lined up along a table adjacent to the girls.
By the second half of the second hour anybody with any chance of success should already be paired off with the person of their choice at one of the corners of the table.
Until recently a popular move by guys who were unable to obtain the phone number of the girl of thier choice (through shyness or general incompetence) was the "guess my phone melody" ruse. The guy-thinking he was quite slick- would get the girl to call his cell phone and see if she could guess what popular song tune would spew forth. The girls' number would then be recorded in his history of calls received. Girls eventually caught on.
When the time comes to pay, the guys rush to the cash register to pay (because that's the manly thing to do) while the girls make totally insincere gestures of trying to pay their share. The girls don't get to pay, unless the fact that one of them has a boyfriend has been revealed, then she will have to pay her own way.
After all, If she has a boyfriend, she has no reason to be there.