In “We Real Cool” by Gwendolyn Brooks, the characters skip school and go to the Golden Shovel to play pool. They are seven teenagers, and they seem to take great delight in their rebellion. They are “real cool,” they proclaim.

These young people “lurk late.” They stay out into the night, probably past their curfew, thinking that they are independent and don't have to follow the rules.

They also “strike straight.” They tell things like they are (or at least they think they do). They seem to have quite a high opinion of themselves really. Alternately, this expression might mean that these kids get into fights when they are offended.

The teens “sing sin.” They brag about their misdeeds. They talk about what they will do next to rebel against adults and against the rules.

Further, they “thin gin.” They drink alcohol, and probably cheap, watered down alcohol at that because it's likely all they can afford and all they can sneak around with them.

The kids “jazz June.” They try to make their lives “jazzy,” exciting, even thrilling. They don't want to be bored. They want to have fun.

Finally, and quite a bit more seriously, the teenagers “die soon.” If they continue along their current path, they are taking a risk, and the speaker seems to realize it. Their rebellion may be rather small now, but it could easily get out of hand, especially with the alcohol. Little acts of defiance lead to larger ones and sometimes serious consequences.