in episode 11 opening scene, the 3 guys was in basket ball game scene.
The 4 guys went camping, but all of them only brought alcohol. they asked the girls next camp for some food as exchange for some alchohol. But the girls already exchanged it with other men (who is younger, in their 20's).
Dojin said that they will win the food in basket ball game.But what he did't realized is their age. They lost not only the game but also all their alcohol.