Brooks has said that she passed a pool hall during school hours and saw some boys shooting pool. Instead of asking herself why they weren’t in school, she contemplated what these boys thought of themselves. She suggested that they wanted to feel contemptuous for “the establishment.” The month of June represents the establishment. The establishment is the prejudice within social conditions that has stifled their opportunities and development. So, they sound contemptuous by declaring they skip school and drink gin. But there is also a plaintive irony here. They don’t want to “jazz June” and “die soon.” They feel that is their only option.
There are seven in the pool hall. This might be ironic. Seven is a lucky number.
"Golden" is also ironic or said with a mocking tone. If the name of the pool hall is the “Golden Shovel,” it is ironic and self-mocking or, once again, mocking the establishment. “Shovel” conjures images of labor, dirt and digging a grave. Hard labor jobs may be all they can get. They are treated like dirt. The freedoms and possibilities in their lives are cut short. If some “die soon,” they claim that their plight is analogous to digging their own graves.
Put "golden" and "shovel" together and you have a paradox: a symbol of wealth and success next to a symbol of labor and death. This is contemptuous and plaintive.